Garden plant landscape is mainly composed of plant configuration landscape and plant color landscape, and they interplay with each other, in which color sense is an intuitive expression that is easily identified and recognized by humans. There are different views on the configuration of garden plants in East and West. During the Renaissance, European gardens were dominated by regular garden, and the color tone was mainly green, which was single. In the era of Victorian gardens and Edwardian gardens, a large number of bright flowers were applied to gardens and became the main elements of garden design. In ancient books of China, plant color configuration was recorded in the Zhangwuzhi Flowers and Trees and Huajing. The color matching of the traditional garden plant design is simple, elegant and far-reaching, and color is regarded as the plant’s own “character”. In the collocation, it blends feelings with scenes, and uses color to set off ambience. Modern researchers in each country further understood and studied plant color configuration. “Color season theory” proposed by American Carroll Jackson in the early 1980s was introduced into China by Ms. Ximan in 1998. In 1996, England color planning expert Michael Lancaster further proposed the concept of “color landscape” in the evolution of color in modern city (Susan, 2007) . At present, there are fewer studies on landscape color application of plant configuration in Tibet at home and abroad.
Plant color is mainly shown by its leaves, branches, flowers and fruits (Zhang, 2015) , in which the color of plant leaves more has viewing characteristics in the time and space. The color area of the colorful plant is greater than that of the flowering plant, and it is easy to form landscape area. Due to the limitation of geographical environment, plant twigs in Norbulingka are roughly similar in color, and their recognition is not high, which is not studied in this paper. Combining relevant literatures, field survey, regional characteristics, and plant configuration mode, 62 kinds of representative ornamental plants were screened out to quantitatively analyze color values of their leaves, flowers and fruits, and carry out color difference analysis.
2. Research Zone and Method
2.1. Research Zone
Norbulingka belongs to national key cultural relics protection unit, and is located in the western suburb of Lhasa. Its construction model represents the formation period of traditional Tibetan garden―palace garden, and it is one of main traditional Tibetan garden forms. Meanwhile, the establishment of Norbulingka also marks the formation of traditional Tibetan garden art (Minamik, 2018) . On the one hand, the construction form of Norbulingka absorbs the characteristic of manor gardens, Zongbao gardens and temple gardens focusing on greening, thereby causing the natural garden features of greenery. On the other hand, the construction pays attention to the overall garden effect, emphasizes the theme of architecture, forms a spatial layout of specific pattern and landscape conception of plant configuration. At plant configuration aspect, Norbulingka possesses rare tree species across the Tibetan Plateau, and there are also subtropical and temperate plants, a total of more than 230,000 trees. Among them, there are national first and second protection tree species (Cupressus gigantean Cheng et L.K. Fu, P. griffithii McClelland, Cedrus deodara (Roxb.) G. Don, Pinus armandii Franch, Sabina tibetica Kom, Xanthoceras sorbifoli um Bunge), tropical plants (Fargesia spathacea Franch, Albizia julibrissin Durazz.), precious flower species Hydrangea macrophylla, and old trees more than 200 years old. Cover area of green land occupies 83% of total, and creation model of whole garden is mainly based on natural garden construction techniques (Xu, 2015; Deng, 2005) .
2.2. Research Methods
Color quantification method of plant landscapewas used in this paper. Using A-6NCS1950 color card (Yue & Song, 2017) , CMYK value of leaf color data of plant in Norbulingka was collected by CAD, Photoshop and EXCEL. By combining dynamic change of plant color, plant configuration and color characteristics in Norbulingka were analyzed.
3. Plant Investigation and Configuration Characteristics
3.1. Investigation of Ornamental Plants
For climate characteristics of Tibet and growth feature of each plant, ornamental plants in Norbulingka were surveyed from September to October 2017 and March to May 2018. The species and color attributes of ornamental plants were investigated (Qi, Wang, & Gao, 2012) , and investigation results were shown as Table 1.
Table 1. Investigation results of ornamental plants in Norbulingka.
3.2. The Characteristics of Plant Configuration form
3.2.1. Dominated by Local Tree Species
The tone of plant configuration in whole garden is constituted by local tree species, to highlight local characteristics, such as the large-area cultivation of U. pumila, P. cathayana, P. alba, F. mandshurica, and S. paraplesia. Especially S. paraplesia in Norbulingka, its shape likes a dragon, and the posture is diverse, which is rare in other places (Minamik, 2018; Wang, 2017) .
3.2.2. Valuing Plant Morphology
Plant morphology is an important link of garden plant configuration, and the isolated plant morphology is common. Using its branch morphology and the difference in flower color and leaf appearance, the style of scenic area is created. This is evident in Norbulingka. For example, Gesang Palace scenic spot highlights the bamboo to express its seclusion; Dadanmingjiu Palace scenic spot highlights pines and cypresses, to illustrate its solemnity; Cuoji Palace scenic spot uses flower sea to render its “heaven and wonderland” atmosphere (Ernie & Tony, 2004) .
3.2.3. Diversity and Unity
Plant configuration inNorbulingka ingeniously uses the textures, colors, lines, postures, etc. of different plants, organically arranges bicolor plants and monochrome plants, large area of green and individual bright flowers, high + low tree species, rude + thin tree species, thereby reaching the unity in the change and the change in the unity.
3.2.4. Valuing Level Contrast Relationship
Level contrast of flowers and trees is used to avoid monotony. Flowers and trees arrangement of Dadanmingjiu Palace at east, west and north are divided into four levels according to plant height. Flower is in the inner circle, followed by Syzygium aromaticum and fruit trees, outer ring is pine and cypress, and the plant height gradually rises from inside to outside. Pterocarya stenoptera is dominant in the forest of east wall, which is interspersed with U. pumila Using the combination of twig height, crown shape, color, sharp contrast is formed (Zhang 2015; Ma & Zheng, 2013) .
3.3. Plant Layout Characteristics of Space Node
Space node of Norbulingka is dominant by the space composition form of point + line + surface (Gong, 2015; Wang, Rong, & Li et al., 2017) . When single attraction is taken as a main node, plant layout is dominated by large arbor position, and it mainly emphasizes that garden trees are dominant by cypress. It is because that Sakyamuni and his disciples had used “cypress seed to hunger”, and cypress is also the symbol of longevity and eternity. Peach is planted in front of the palace gates, and they are 7, 8, 15, 18 or 28 respectively, with the meaning of blessing. For example, Gesang Palace uses the plant configuration form of pine + cypress + walnut, playing the role of radiation from space composition. Norbulingka has two kinds of road layout models. One is ring, and it is dominant by turning road, meaning “reincarnation”. The other is line layout, and it mainly plays the space function. At this place, common plant configuration is hedge + flower, playing the role of “connection” from space composition. Large-area U. pumila and Armeniaca vulgaris Lam. are also cultivated in Norbulingka, mainly playing the roles of spaceseparation, delineation of scenic boundaries, barriers in space composition (Zheng, 2017; Lin, 2017) . Plant layout model in three kinds of space nodes are shown as Table 2.
4. Statistics and Analysis of Plant Color Value
4.1. Investigation Statistics of CMYK Value
Combining the data, color characteristics of leaves, flowers and fruits from each ornCMYK has the characteristics of high color identification and high color resolution. It can perform objective quantitative analysis and qualitative evaluation of color, and has scientific value and verifiability for monitoring the dynamic change of the seasonal color of plants.
Amental plant in Norbulingka were collected and analyzed from September to October, 2017 and March to May, 2018. Moreover, CMYK value was extracted by the related software, and result was shown as Table 3.
Seen from Table 3, CMYK values of ornamental plants in Norbulinkaare richer, in which green line in leaf color value is the most, a total of 50; there are 7 red lines and 17 blue and violet lines in flower color value.
Table 2. Plant configuration at main nodes of Norbulingka landscape area.
Table 3. Color difference values of leaves, flowers and fruits from each in ornamental plant in Norbulingka.
Note: E. pulcherrima belongs to potted plant. According to field survey, a large number of E. pulcherrima appear in Norbulinka. Started from landscape color use angle, E. pulcherrima is listed as ornamental plant for unified investigation and analysis.
4.2. Analysis on Leaf Color Values of Ornamental Plants in Norbulinka
Seen from Figure 1, percentage of purple herb = red shrub; cyan herb > light green herb; dark green arbor > grass green arbor; yellow shrub > jade green shrub; bitter orange arbor < bottle green arbor.
4.3. Analysis on Flower Color Values of Ornamental Plants in Norbulinka
Seen from Figure 2, percentage of bitter orange herb < blue shrub; cyan herb > light green herb; dark green arbor > grass green arbor; yellow shrub > jade green shrub; bitter orange arbor < bottle green arbor.
4.4. Analysis on Fruit Color Values of Ornamental Plants in Norbulinka
Seen from Figure 3, percentage of purple shrub > yellow shrub; yellow arbor > red arbor; blue arbor = green arbor; red shrub < green shrub,
5. Results and Discussions
The results showed that 1) in color values of leaves, percentage of purple herb = red shrub; cyan herb > light green herb, dark green arbor > grass green arbor,
Figure 1. Difference analysis of leaf color values of ornamental plants in Norbulinka.
Figure 2. Difference analysis of flower color values of ornamental plants in Norbulinka.
Figure 3. Difference analysis of fruit color values of ornamental plants in Norbulink.
yellow shrub > jade green shrub, bitter orange arbor < bottle green arbor; 2) in color values of flowers, percentage of bitter orange herb < blue shrub, cyan herb > light green herb, dark green arbor > grass green arbor, yellow shrub > jade green shrub, bitter orange arbor < bottle green arbor; 3) in color values of fruits, percentage of purple shrub > yellow shrub, yellow arbor > red arbor, blue herb = green arbor, red shrub < green shrub.
The investigation time lasted for 4 months, which did not form complete cycle and could not completely reflect dynamic color change of ornamental plants in Norbulink. Meanwhile, the weights of perennial herb and tree change with time goes by, as well as its flower, fruit, leaf, twig and bark, and it needs further exploring the whole impact of plant color in Norbulink.
Based on the research, it could further study dynamic color changes of ornamental plants in Tibet theme park by quantitative analysis method.
Plant configuration in Norbulink combines Chinese gardening techniques, and a lot of local tree species are planted according to local situation. Meanwhile, the introduction of numerous exotic plants is to better use garden features. Based on prior investigation, plant color data in Norbulink was collected. Combining dynamic change of plant color, plant configuration and color characteristic in Norbulink were analyzed. Plant color data collected by CMYK as the basis of color design of plant landscape has the characteristic of qualitatively and quantitatively expressing color composition, and is the optimization method of scientifically and reasonably expressing color design of plant landscape. Color difference analysis method in this paper has certain research significance for the plant configuration and color matching of plateau garden landscape.
This work is supported by the Supported by Open Fund of Tibet Plateau Ecological Security Joint Laboratory (STX2018-02), Research Project of Tibet Autonomous Region on College Humanistic and Social Sciences (sk2015-38), MOE Youth Find Project on Humanistic, Social and Scientific Research (13YJC840020), 2015 Landscape Construction Project, and 2016 Higher Vocational Technical Education Quality Promotion Plan on Landscape Technology.