scale-color is a primitive that reports a shade of a color proportional to the value of a given number. For example, if we wanted to create a traffic model in which cars with fuller tanks were brighter than those with emptier tanks, we would write the following code:

ask cars [
    set color scale-color white tank-level 0 100
]

Or if we wanted to model a flock of sheep where more lush patches of grass were brighter than those that have already been eaten, we would write the following code:

ask patches [
    set pcolor scale-color green lushness 0 100
]

Things to keep in mind when using scale-color:

• The syntax of scale-color can be hard to remember. It is as follows scale-color base_color exact_point lowest_value highest_value.
• You can think of the base_color value as the middle point in the provided range. For example, if we wrote scale-color green 50 0 100, we would get exactly green.
• Don't forget that the desired base color comes first, then comes the exact value , number is the value you wish to scale by (usually a turtle or patch variable), and range1 and range2 are parameters for describing the minimum and maximum values of number. If range1 is less than range2, then larger numbers result in brighter colors, but if range2 is less than range , larger numbers result in darker colors. If the number is outside of the range, then either the lightest or darkest shade is chosen.
• By default, scale-color produces darker shades for smaller values and lighter shades for larger values. However, it is possible to reverse this by writing the maximum value as range1 and minimum value as range2 such as scale-color lushness 50 100 0. We are doing exactly this in the model example below for the nutrition level of each patch.

In the model example below, we use scale-color to adjust the color of each patch to reflect its nutrition level (1 being lowest, 5 being highest). Each time our farmer moves onto a patch, it checks the nutrition level there. If the nutrition level is above 3, the farmer plants a vegetable. We also color the vegetables using scale-color based on the nutrition level of its patch. The vegetables that get more nutrition have a brighter green color.