Hypomelanism loosely means reduced melanin (black). In the corn snake hobby we chose to give the name Hypomelanism (abbreviated, HYPO) to corns that owe their reduced black to one of the several Hypomelanistic gene mutations, BUT a snake can have reduced melanin without the impact from a mutated gene.
These two snakes (Striped Amel and Striped Hypo) demonstrate the sometimes similar degree of reduced melanin. Naturally, Amel (aka: albino) mutants have NO melanin (demonstrated by eyes not having any black), but some Hypo corns can have so little melanin that they can resemble the Amel mutants, but with dark eyes--which, of course, demonstrate the presence of melanin, if only minute melanin volume. BTW, the eyes of albino/Amel snakes--and other organisms--are red, generally because of the blood they contain.