But he has worn darker colours before and I don't remember seeing him this wet before. But it's possible blue shows it more since it's not as dark as the colour black. Also, he could be taking some sort of supplement that makes him sweat more these days.
He was out for a month. Practising isn't quite the same as playing, maybe he's just getting a wee bit more anxious then he usually would, therefore sweating a bit more?
Whatever it is, he'll be fine for Wimbles.