Turned white overnight?

My lower leg hairs turned white overnight. Nah, just kidding, they turned white in less than an hour. How come? Cutting/sawing granite with short trousers did it. The dust blew, amongst others, to my legs :) The extra shows at the top left how that looked.
Of course Caspar needed to watch closely what I was doing. A bit annoying, such a boss :)
The west wall is standing now too, needs only mortar. That will come tomorrow. And then we can start with the finishing touch. I will probably take a picture when the patch is (nearly) ready, from a ladder or so.