I am not making the B/U lens area into a turn signal, it will still be a B/U light and I just might use any color I decide on as to alert that I am backing up
That's an effective way to cause a crash and have your insurance claim denied. Color is one of the ways car lights convey their message, which needs to be unambiguous. We don't get to pick random colors because we think purple back-up lights or green brake lights would be cool.
They're not required to be. It's nice when they do, but the regs are written such that the main function of the backup light is to warn others that you're reversing.