Color theory - complementary color

I don’t quite understand this theory from :

If a doctor stares at blood all day (dark red) and closes his eyes, he’ll see the “opposite” of that color. In this case, that would be a light green. For this reason, the common color of hospital scrubs is a light green. While it may not be rocket science, this kind of “complementary” color system actually calms our visual system. If the people engineering the color at a hospital can derive benefit from color theory, then web designers certainly can!

Why should hospital scrubs be light green? When doctors go to sleep, don’t they see blood red and get nightmares?