I cannot call a chalkboard a blackboard any more in case it offends
Who says you can't, theres no derogatory inflection, inference or intent in describing a blackboard as a blackboard, it has no historical, cultural or literal relationship with black people. There's no rule about it anywhere, and no desire from anybody for there to be one.
but I can call a wipeboard a whiteboard.
Now thats bang out of order, how dare you make such a slur on my peelywally northern european heritage by using the word 'white' to describe a bit of formica that you scribble on with a pen.
It a case of political correctness made up