Choosing Cmd > Color will bring up two windows that allow you to choose and create your own color schemes. There are 6 distinct areas that you can set independently: Letters, Commands, Message Area, Word List, Short Words, and Browse.
First choose the area you want to change. Its current color (foreground and background) will be shown in the large square area with the big 'A'.
Choosing Fore or Back will then allow you to change the foreground or the background.
The simplest way to change colors is to simply pick them from the 120 assorted colors in the palette on the left. Pause over the color you wish and it will be chosen. If you wish, you can modify it as described below.
There are 8 colored rectangles beneath the large square. By pausing over these areas you will incrementally add or subtract red, green or blue to the current color. The white and black areas will lighten or darken the color. Note that white is maximal red/green/blue and black is minimal red/green/blue. Red plus Green makes Yellow. Red and Blue make Purple. In this way you can make any color you wish!
When you have finished with the color selections, you can put them into place by choosing Done. If you wish to forget all the changes, choose Abort and all will be abandoned.