Doris Day '69 Ragtop

Both California black plates and blue plates were issued to new cars in 1969. The previously-owned '69 340 Swinger I purchased in November 1969 had black plates. The plates were toward the end of the black plate era because the first letter on the plate was a 'Y'.
I think this is black, and going along with your logic, the "Z" would be late in the sequence.

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