The black hair colour has a weird blue tone to it and the platinum blonde has an odd green. The yellow yellow hair is just bad. The only natural hair colours that I use are the dark brown, the middle ginger and the middle blond. The black eyebrows look terrible on darker skin tones. The salt and pepper hair has a better black to it than the actual 'black' hair. The unnaturals are fine but we need more variety in them.
The only way I could imagine it being fixed is with a colour wheel (the same with skin tones) and options to pick what ombre colours the hair has (as I have to use CC if I want my sims to have different hairstyles per outfit and I know that option isn't availible for console players)