Makes all the difference where you live. Like the guy above said, it is NOT legal in ontario and you definately will get pulled over, because thats like the easiest ticket a cop can give you next to expired tags.
Its actually not even legal in California, and im pretty sure its not done too often anymore now that they actually are issuing personalized collector plates. The whole deal was that they didnt used to be able to get you a collector plate (black plate) AND have it personalized. Now they can, so that trend of painting regular personalized plates kinda died off. There was an article that glossed over this in the christmas issue of Motorcycle Classics.
I just reread your post and it seems like you are in California. The only flaw to your plan is that cali collector plates are Black/Yellow, which you could probably get away with painting (or you could just buy one...). You want to do black/orange, which will stick out like a sore thumb and probably make you an easy target for cops looking to fill their quota. I dont live in Cali, so maybe the cops there dont really care, but i probably wouldnt do it because itd just end up being a hassle.