That is mocking a person for his / her hair colour.
When I was a lad growing up in Liverpool, (Skitting Capital) It was a free for all! It mattered not what retort I used as a come back from the many red hair jibes I received. Now its not such a level playing-field though is it! and I see on here some are more than happy to draw attention to a persons hair colour as a way of demeaning them as a person, in the normal way, you know subtle like.
Ginger bashing is alive and well here as it is all over and its acceptable by all and everyone unless you are the recipient of course. If we truly want equality then it should be just as repugnant to call people for the colour of there hair as it is for the colour of their skin, the appearance of their eyes or anything else for that matter.
A recent conversation with a bobby who informed me of all the things that were now classed as hate crimes, including verbal attacks on disabled people (who does that?) slagging off anyone because of hair colour is not one of them. unless violence or threat is felt by the recipient.
Equality, so far to go..........