The reason that I think Denisovans still would have blond hair is that the genetic irregularity causing Solomon blond hair is impossible to find unless it's being looked for, otherwise their genome is the same as someone with brown hair. The genetic study probably got the girl's hair wrong.
Keep in mind that we know some Neandertals had red hair (independent mutation from modern human red hair), and others had brown hair. So it's possible some Denisovans were blond, and others were not.
That said, the archeogenetic information suggest Denisovans went through a much stronger bottleneck than Neandertals, meaning its plausible to assume they might have lacked (at that point, at least) notable "races."