For my bikes I have black and white for pre 75 bikes
And yellow black onwards..
I had this discussion with a mate the other week ..He wants a black and white for his 76 bike he has restored to near standard...I said nobody in 76 would put a b/w plate on a new bike as it would've made it look old and in 76 everyone binned them and would've wanted yellow plates to make them look modern and new...
Since then he went out and ordered a black and white plate anyway so just goes to show what do I know.
And i agree don't give the old bill any excuse to pull you..but I would imagine if it's a correct size not a minute postage stamp they wouldn't be that bothered as now days our bikes just look old /retro