iPhone 4 restarts every 3 min
Did your iPhone was jailbroken before the color swap?

If so, I'm afraid you broke something inside the phone. Something the OS is trying to access and since it's broken, respring the springboard (maybe that's a bug, but since you're not supposed to fiddle with the inside of the phone, it's not something you could use to replace it).

As a last resort, you could try to reopen it and see if there's anything that looks broken.