Certainly the old Brighton Borough force used to issue black painted chrome QC plates. It was common practice for recruits in the 1960s to be given two chrome plates & be told to paint one black for night duty wear. I uzsed to think that this practice had been running for many years, but recently saw a photo of a pukka black QC plate with chrome arms centre. So I suspect that at some point the force ran out and instead of buying a new batch of black plates just told recruits to get on and paint theirs. Later, in the 1980s and 90s for sure, the Sussex Police specialist firearms team wore a black cap badge. This I know was just an ordinary chrome QC badge sprayed with the same satin finish black cellulose paint that the force armourer used for painting the guns. But, as for other forces, I'm not sure...