Nothing you can do at this point. If you had the original plates and can document that they were previously on your car, you can get them re-issued to your car, although it usually takes jumping through a lot of hoops.
The last 2 years in a row, Goobener Davis has vetoed a bill to allow us to put black plates back on our classics, because he's complete idiot (but at least he has perfect hair). The bill both years was endorsed by the CHP and DMV, and passed unanimously in both houses before getting axed on Davis's desk on the last day that he could vetoe them before they became law.
With the upcomming recall, maybe next year we can put black plates back on our cars