When there is a large population of rabbits in an area, the rare colour forms can be evident. When rabbit density is low, rare colour forms are unlikely to be detected, but they are still present. So if you see a rare colour form, it may be that you came across it by luck in a low density population. The popular sayings that unusual colour forms result from inbreeding and that rare colour forms prove rabbit density is high, are both likely to be myths imo.