Why can't I register my bike with a California Black & Yellow plate?

Why dosent the Department of motor vehicles let you register you classic 60s motorcycle or motor scooter with a correct era license plate, Im talking about the California Black & Yellow license plate? My bike looks crapy with the new ones.

I have an original plate

Very simple answer, they don't make the black and yellow plates any more.

It's the law.

You don't have to keep it that color. You can paint it black and yellow. License plates are issues in the current color but, as with anything else, it does not have to stay that color.

you really consider a 60s model a classic?

I'm pretty sure that if you can find an old plate from the same year (stamped on the plate) as the bike you can register it as a vanity plate.