You can use the <Color> tag to change the color of bodies:
<Body>
<Appearance>Spacecraft</Appearance>
<Name>L5</Name>
<Action>L5=Earth, Moon</Action>
<Color>Blue</Color>
</Body>
This example is from the file:
Lagrangian Points - Earth & Moon.xml
There are 3 types of values accepted by <Color>:
- Named Vales: Red, Orange, Yellow, and a few others
- RGB Values: <Color>255,128,0</Color>
- Hex Values: <Color>FFAA44</Color>
Although it appears that the color is overridden if it is a star (as the color is calculated to be representative).
I'm sorry it's not working for stars; I've made a note to fix this in the upcoming release.
(And thanks for helping me find a bug.)