In my 20's I've done a lot of web design for about 5 years. After 2, maybe 3, years I could "see" the colors and their nuances in the hex codes. More interesting was the reverse lookup, seeing a color and visualizing the hex for it. Fun times. Not sure I still can do it...besides the most obvious ones. But then I was not bad, about 90-95% accuracy ( measured on the deviation of the light/color wavelength ).