Color lookup tables enable you to assign a fixed color to each value of a given field. For example, you might want a certain sales rep to show up as a certain color across all of your reports.
To start with, go into your data source and click on the Create button, then choose "Create Lookup Table." Choose the field you want to color and choose "Color" as the lookup table type, as shown below:
Next, you can assign colors for each of your possible values:
Once saved, try using the field in a report and you'll see values shown with the specified colors: