If you name your bot cheatbot2 you will unlock a few cheat components.
Here's how I make a custom skin:
1) Paint each side of your robot's body a different color, and remember which is which.
2) Add one or two layers of dark edges
3) Hit "export texture" and give it a name you'll remember. Make sure to check off "export current texture instead of a default one"
4) Return to your desktop, and in your RA2 folder, look under "custom textures" and find the name of your file. Open it with any program that can handle BMP's.
The file will show you each side, with the dark edges indicating boundaries. Edit it as you wish, save, and return to the paint shop, and hit "import texture." You should be all set.
Important: Do not adjust the size of the picture or your texture will come out looking messed up.