Game keeps changing my sims hair colour.

I have a young boy sim and I want his hair to be black, but whenever I go to another outfit it changes colour to red haired or blonde. So go and 'change appearance' and alter his hair again for each outfit making sure it stays the same throughout each outfit change. Which it does. But now I've gone back to play it his hair is now blonde. Dunno how to fix this :/ I am not using any CC for him.