The color of his hair is nothing correlative to his intelligence! Or it might be. It probably is. He hasn't thought about it much. He doesn't worry about his intelligence too often, aside from when he's trying to piece together complex sentences delivered at gunpoi--hi, gunpoint! He's smart enough at least to get his hands up, even if he does take a moment to actually process the spoken bit.

But he processes it eventually. Sherlock will probably <>see the moment that it happens. It comes with a smoky smile and widening eyes. "You ain't gonna shoot me. Jeezis, how old's that thing?"