Can a blond and a redhead have a brunette child?

yes, I'm studying it in Biology right now, both parents carry the gene for brown hair then its possible, for an example,

purple is incomplete dominant over white for flowers

this is thekey

PP- purple

Pp-pink

pp- white

and say you cross to pink flowers, Pp x Pp = PP, Pp, Pp, pp to solve is very simple, its just like lattice multiplication one letter for each square