the whole situation is even more tricky than meets the eye ... To wit :
Here's a fairly comprehensive rundown of Ca's plates' colour-to-year , etc.
Black with Yellow Characters : 01-01-1963 through 31-12-1969
Blue with Yellow Characters , 6 digit : 01-01-1970 through c.1980
The 1st letter indicates the plate's year-of-issue . For example :
337 GBL . G = 1972-issue
Your '73 Duster -should- have originally had a plate with its 1st letter being "G" , "H" or possibly "J" ( "I" wasn't used as a 1st letter ) , being preceded by 3 numbers ; example :
726 HYH . H = 1973-issue
Certainly , black / yellow plates did indeed appear on certain early-build , early-sell 1970 models ( I've seen no less than 2 different 1970 Darts with black/yellow "Z"-series plates ) , and on the contrary , seeing 1969 models with blue/yellow plates
( there's a '69 Camaro around here that was built in Dec '69 and sold new in Jan '70 . Its plates are blue/yellow and start with "A" as the 1st letter ) .
1970 was also the first year for personalised plates ;
1980 was the year that plates went to a 7-character arrangement ;
1982 was the first year for the "sunburst" plates ( ornate , art deco-era "CALIFORNIA" with the "O" as the Sun ) ;
1986 was the last year for blue/yellow plates ;
1987 was the year that the white / red "CALIFORNIA" / blue characters plates were issued ;
1993 was the first year for the cursive "CALIFORNIA" , the one that's still around , and is ugly as **** .
For such a car-culture-rich state , we certainly have the most boring , ugly , uninspired license plates , BAR NONE !
To answer your question : Do. Not. Change. Your . Plates' . Colours . You WILL get nailed .:glasses4: