For the state to actually produce these legacy plates, a given color scheme had to receive 7,500 pre-orders from January 1, 2013, through January 1, 2015. That seemed pretty doable given Californians reputation for loving their cars, but according to Truck Trend the program hasn't exactly been a raging success. It claims that only the yellow-on-black tags have received their requisite applications. Black-on-yellow has managed around 2,000 requests, and yellow-on-blue has received about 1,700 of them.
The lack of popularity for the yellow and blue tags makes some sense because enthusiasm for restoring models from the '70s and early '80s is just starting to build. However, it seems like owners of '50s classics would be eagerly hopping onto this program. Perhaps many of them still have their original black plates and don't need a reproduction. Obviously, there are still a few months to go for the other two schemes to meet their requirements. Applications are still available, here, and if a design doesn't nab 7,500 orders the $50 pre-order is refunded.