A color scheme is a range of related colors that can be applied to a collection of features, rasters, layout graphics, or symbol components. Color schemes contain at least two colors; the transition between pairs of colors can be either a continuous gradient or a discrete boundary with no blending from one color to another. Color schemes can also be random, where a variety of colors residing between two defined colors in an HSV color space make up the scheme in a random order. Color schemes of differing types can be appended together to make complex collections of colors called multipart color schemes. Color schemes can be stored in styles for reuse or sharing.
Color schemes are called color ramps in ArcMap, ArcScene, and ArcGlobe.
Continuous color schemes
Continuous color schemes show a smooth gradation of two or more color stops. Each color stop is defined by a color and its transparency, and a position along the scheme defined as a percentage of the total scheme length from left to right. A stop is always located at each endpoint, at positions 0 percent and 100 percent; the color and transparency of these two stops can be changed, but their positions cannot. A stop is the specific point where the blending of two adjacent colors in a gradient ends. You can move stops interactively by clicking on them, even changing their relative positions by dragging one over the top and beyond another. You can further customize color schemes by adding or removing stops or by reversing the order of all the stops. Check the Evenly distribute color stops box to arrange all stops evenly along the length of the color scheme.
The segments between color stops also dictate the appearance of a color scheme. The selected segment is shown by a black bar to the left of the selected color stop. Color scheme segments have two properties: the algorithm used to determine the path traversed through the color space between the two stop colors (HSV or CIE Lab) and the polar direction which determines the direction traversed around the color wheel for variations in hue (shortest path or longest path.)
The appearance of segments in a continuous color scheme is determined by the algorithm that calculates the interim colors between the two surrounding color stops.
The HSV (hue, saturation, and value) algorithm is a linear traverse through the color space between value pairs: a linear path from the hue of color 1 to the hue of color 2, a linear path from the saturation of color 1 to the saturation of color 2, and a linear path from the value of color 1 to color 2. It is conceptually easy to understand, but since all intervening colors are shown, it is not always the most suitable for quantitative rendering.
When a segment uses the HSV algorithm, the Polar direction dictates whether the path from the hue of color 1 to the hue of color 2 will follow the shortest direction around the color wheel (the default), or the longest. The polar direction pull-down menu illustrates this choice graphically to guide your decision. Understand that when one or both of the color stops on either end of the segment has no hue component (whites, grays, and blacks), the polar direction setting will have no effect because there are no hues to blend between. When a small hue value is present, you will see some differentiation in color progression when changing the polar direction. For this reason, HSV color schemes that traverse through low-hue colors may appear differently from their color ramp counterparts in previous versions of ArcGIS.
The CIELab algorithm blends two colors without traversing intervening hue space, resulting in a smoother progression from Color 1 to Color 2 than the HSV algorithm produces. In many cases, this produces a very desirable smooth scheme between two colors, but intermediate color values can be very gray (low saturation) if there is a great difference between the two colors. Polar direction is disabled for CIELab segments, since this algorithm always follows a direct path through the color space.
Discrete color schemes
Discrete color schemes consist of two or more solid blocks of colors with no gradation between them. The blocks are synonymous with the color stops in continuous color schemes, but they have only color and transparency properties. There is no concept of a color scheme segment in discrete color schemes. You can rearrange the order of the blocks by clicking and dragging. You can further customize discrete color schemes by adding and removing blocks or reversing the order of all blocks.
Random color schemes
Random color schemes do not contain color stops, segments, or blocks. They are defined solely by a minimum and a maximum HSV color. The scheme is compiled of discrete hues that are generated randomly so that their H (hue), S (saturation), and V (value) settings lie between the H, S, and V values of the minimum and maximum colors, respectively. A single transparency value is applied to the entire scheme. Random color schemes do not include any selectable components along the scheme preview. The appearance of the color scheme is dictated by the HSV values specified as minimums and maximums from two color pickers.
Random color schemes are regenerated each time they are opened or applied. You can regenerate manually to form a new arrangement of random interim colors between the minimum and maximum values. This updates the seed value. If you find an arrangement you'd like to return to, note the seed value and re-enter it when you apply the scheme.
The color of the minimum and maximum colors are modified by choosing colors from the color picker or by clicking More colors. Regardless of the native color model of the selected color, colors will be converted to the HSV color space, and those respective values will be used as the limits for all interim colors generated along the scheme.
Transparency does not vary along the length of the random color scheme; it is a single value applied to the entire scheme. The default transparency setting is 0 percent, which is fully opaque. Transparency is indicated visually in the scheme when an underlying gray checkerboard shows through.
Multipart color schemes
Multipart color schemes consist of any combination of two or more continuous, discrete, or random subschemes. Subschemes are identical to their stand-alone counterparts, except that continuous color schemes within a multipart color scheme contain only two stops. A multipart color scheme cannot contain another multipart color scheme. A multipart scheme can contain a maximum of 20 subschemes. You modify the subschemes one at a time. Click the back arrow to return to the whole scheme. You can delete or reorder subschemes, or add new ones.
Continuous subschemes contain only two color stops, one at each extremity of the subscheme. The Add color button, Remove color button, and Position spinner control are not present in the continuous subscheme component. A multipart scheme that contains only continuous subschemes, where each end color is equal to the subsequent start color, will be converted to a continuous scheme when it is reopened.