I cleared out the ugly raincloud thingy from a previous poster's Stars mod and created this thing -- very easy on the eyes, i think. Right click to save it, rename it bg.jpg and drop it in the C:/Program Files/PokerStars/Gx/ (replaces the existing default bg.jpg background image)
IMPORTANT: The Stars client reloads the default images every time you run the icon that the default installation places on your desktop...so DON'T use that icon to run Stars. Instead, go into the Program Files/Pokerstars folder, and find the PokerStars.exe program AND NOT the PokerStarsUpdate.exe folder. But the former on your desktop and use THAT to run the client when you want to play. Then, every so often, backup your modified background, run the PokerStarsUpdate.exe program to check for updates, and then go back and put the mod background back in the Gx folder as described above.