It's a combination of brown, peach (the colors from the original 'human skin tones' Ubuntu concept) and orange/red (newer, based on the Canonical logo).
I actually tried to organize a theme contest in conjuction with DeviantArt for 8.04, working with Ubuntu Artwork team, with prizes etc.
The first thing that happened was that winners were limited to working with the existing palette. The directive comes from Mark Shuttleworth and Ubuntu art are powerless to change it. The contest didn't go ahead.
However Mark seems to have recently changed his mind.
I actually tried to organize a theme contest in conjuction with DeviantArt for 8.04, working with Ubuntu Artwork team, with prizes etc.
The first thing that happened was that winners were limited to working with the existing palette. The directive comes from Mark Shuttleworth and Ubuntu art are powerless to change it. The contest didn't go ahead.
However Mark seems to have recently changed his mind.