It’s not compulsory 😬 but ND people in general do tend to be a bit more outside the box, and a bit quirky in different ways. And ADHDers are obviously more impulsive and risk taking and like novelty. So I wouldn’t be surprised if this might translate as into a bigger proportion using colourful hair dye. I used to dye my hair bright colours. Not so much now I’m older though. Of the ND people I know many of them dye their hair colourful colours, and of the ones that don’t, it would surprise me if they did if that makes sense!