Color files contain the sets of colors that World Builder uses. In fact, they only contains seven colors, but these colors are interpolated to produce the smooth gradient coloring that you see on the maps.
World Builder comes with a set of default color files. Click the 'select' button beside the file name to see and select from the available files:
Colors can be edited, and new color files created, using the Colors File Editor, which is available from the 'edit' button beside the file name:
See Colors File Editor for more information about editing the colors.