Even if they see in shades of gray, your blaze orange may be a different shade of gray than the foliage around you. I don't have to wear orange in these parts, but if I did it would be camo-patterned orange.
Some time ago I read an article by some expert who had "done a study" - don't remember the details - and this guy maintained that with a deers eyesight, the color blue should be avoided at all costs. Apparently, that color stands out well against the shades of gray they can see. I stopped wearing blue jeans when I read that.
Keith