i stopped racing in about 1972, then got back into it about 1990. Up to about '68 i rode a tiger 70,[250] aB31 [350] and a B33 [500] they all had ACU approved racing No 883 all black number on yellow plates. I sold the B31& the tiger 70 by about 1970, i don't remember noticing the different colour system on the smaller cc machines from NSW until i got back into it in the '90s. As an aside, the colouring system had to come 'cause even in those times 500cc B33s occasionally won the 350 class, because the only external difference was the room for a little finger to pass between the barrel bolt and the cylinder barrel on the 350.[My 350 bsa wasnt very fast, mainly because it was never more than 348cc and as heavy as lead but it still got me into B grade.