How well do you see color?

It happens. A brilliant designer I used to work with (who got a 4 on this test, which shocked me) once reported an issue on a template I coded because the hex value I started a subtle gray gradient with was off by like two ticks. I couldn't believe it -- I created a giant graphic with half of it the color I used and half the one she expected and I still couldn't see the difference. I showed it to a handful of people and only one could tell there were two colors on the screen. I thought it was so crazy that she could spot the difference when the real thing was only a few pixels.