The Starmap display forms a map of your planets and ships relative to their surroundings. At the beginning of the game, color-coding according to a default color scheme are applied to each object on the map. These defaults can be seen here:
If you wish, however, you may make certain changes to the displayed colors. Individual planets can have their colors manually changed on the planetary interface display; alternately, entire player races can have their color palettes changed via the Diplomacy interface on the Dashboard. Colors will be applied in the following order; later changes will over-write all earlier ones.
To change the color of an entire player race, go to the Dashboard and select Diplomacy. There will be a list of players (not including oneself), and the second column will be a clear box labeled "Color". Clicking on the Color box will open a palette; simply select a color and the palette interface will automatically close. To clear a set color, hit the Clear button on the bottom of the palette.
To change the color of a single planet, go to the Starmap and select the planet in question. (Alternately, it can be chosen from the planetary list on the Dashboard.) On the Resources bar is a button marked "Notes"; clicking that will reveal a note pane. At the bottom of this is a hollow box under the label "Custom Color". Clicking on the Color box will open a palette; simply select a color and the palette interface will automatically close. To clear a set color, hit the Clear button on the bottom of the palette.
The default palette, which includes one's own default colors and those for such items as Ion Storms, can be changed through the Settings interface of the Dashboard.