"What color is his hair?"
Translation:Jakiego koloru są jego włosy?
If you mean writing, I think that http://sgjp.pl/ might be a great help to you. It is by far the biggest dictionary of Polish online (with 455.560 entries and counting). It does not define the meaning of words (just shortly, sometimes) - but it lists ALL their grammatical forms; for words that may have different meaning (e.g. the same word being a common noun/a male family name/a female family name ) - it has as many entries as necessary in given case. For instructions, see here: http://sgjp.pl/instruction/