Bee, most everyone (pilots) does what you say (above 10k and not 5.) The key words are "night" flying where color perception is more affected ...but, I gather most VFR does not happen at night anyway. The other key word is "subtle" loss of color vision. The explanation to me was that this would not be problem in familiar surroundings, but if you were flying in a novel situation (ie, different plane, new runway, or inclement conditions ) then you would not want to miss any visual clues, no matter how minor.
