Too tired/drunk to coherently search through the forums to find a potential answer, so here goes I guess:
One of two things seems apparent with my recent milling percentages when looking for icy pigment:
Either I have hit an extreme streak of bad luck and get little to none icy pigment (hovered around 1 in 40 herbs, 1 in 8 mills, when I did it recently, and this is from a large sample of mixed herbs, about 400, 80 mills) (also have hit this bad the last couple of times I did it also, however I wasn't able to document the numbers)
or: Blizzard changed the percentages with which you get icy pigment from milling.
If this is a noob change I somehow missed then cool, just wondering if I am an unlucky poopface.