In addition to its roles in urban settings, color also affects people's feelings and their assessments about the environment's quality. There are no control programs of building exterior’s color in urban planning policies in Iran. Color design of building exterior is done based on the designer’s taste, regardless of user’s preferences. These issues have caused public dissatisfaction with their visual quality. These factors remind us of the need to pay attention to building exterior color, based on the user's evaluation. To evaluate the color of the buildings' exterior, we must describe and classify its color combination. In color evaluation studies, there is no theoretical consensus on the emotional scales of the color description and the components affecting their assessment and definition, unlike physical dimensions of color. Therefore, the questions which arise are: what are the emotional scales of the color description of building exterior? And What are the components affecting the assessment to define and classify the color combinations of building exterior? In this regard, research aimed to identify and determine components describing and defining the color combination of building exterior as harmonious and contrasting. To achieve this purpose, we have used a combination of qualitative and quantitative methods. First, content analysis and then Delphi survey was done by 20 experts in design and color. Having analyzed the results through Q-method, three scales, harmony, temperature, and weight, were extracted to classify the color combination of building exterior and several selected building exterior images of each scale. Due to the wide range of topics, we examined only the harmony-contrast in this research. In the next step, we determined components to assess the harmony of the building exterior's color combination through semi-structured interviews with five architects and urban planners. According to the qualitative results, we used the Delphi survey to confirm these components. A questionnaire was prepared based on these components and selected images of the harmony scale in the first survey. Twenty former experts completed this questionnaire. We extracted the components affecting the building exterior's color combination's assessment harmony by analyzing the data through Q-method. Quantitative values were obtained using the color strip method and HSL codes and based on the components. These values defined the harmony-contrast scale of the color combination of the building exterior. Significant components were the difference between the hues' luminance, the difference between the hues' saturation, the number of the hues in combination, and the color of openings. The form of openings, the formal composition and details of building exterior, and the area of openings and hues in combination did not have any significant effect on the harmony assessment. Therefore, to describe and classify the color combination of building exterior as harmonious, the color combination of building exterior should have a maximum of two or three hues and the same temperature. The difference in luminance between the hues of the combination should be less than 20%. The difference in saturation between them should be less than 15%. The color temperature of its openings should be the same as the temperature of other building exterior colors. The color combination of the building exterior as contrasting should have a maximum of two or three hues and different temperatures. The difference in luminance between one hue and other hues should be more than 45%. The difference in saturation between this hue and other hues should be more than 20%.
