If a child has ginger hair, each parent must carry the ginger gene even if they themselves are not ginger.
For example Brown=B and Ginger=g
Two parents have brown hair, the obvious hair colour that the child will have is brown as both parents have the brown hair gene. This is not always the case, and so the child may get a different colour, in this case ginger. To write the genes basically you can say that Brown=B and Ginger=g. If two parents have brown hair and have a child that is ginger , it means that their hair gene is this Bg. This is because Brown hair is dominant so with overpower the ginger gene giving the parent brown hair. However if two parents have the Bg gene, the hair gene the child gets could be BB Bg or gg. If it gets the 1/3 chance of having the gg gene, the child will have ginger hair. If it gets BB or Bg it will have brown hair. Both Parents MUST have Bg or it wouldn't work.
If two parents both have ginger hair the child will be ginger.
It sounds complicated but i think that makes sense...