Note here that the "blue gene" is NOT sex-linked! Men and women can be "blue blind".
Give me a good heavy fog, a dreary winter's day that starts at 10:30 AM and is gone by 1:30 PM, and anybody painted blue is invisible! About the only thing I can see is the red veins in the whites of their eyes!
Tells me the Picts had to wear eyecovers as well to avoid that extra pick-up on the "red".
The Romans just had to love these guys!