This one's easy!
....and it will surprise you!
I work in retail hdwr./paint...12+ yrs. now!
What color is the blood in the back of your eyeball, where blood-vessels are the densest? Obviously....RED!
Yeaars ago, when learning how to adjust paint colors, adding green will correct some colors if they're too red. Green is opposite of Red on the color-wheel.
See where I'm goin' with this...
STRONG light sources can "overwhelm" the red-vessels in the eye. So...if Red is taken AWAY, our vision temporarily skews toward Green!