There is plenty of evidence in the StarWars universe of DarkSide corruption, on various planets area's rich in the DarkSide of the force have mutated plants and animals into stronger more vicious versions of themselves. The Sith Pureblood's colour is not affected because their ancestors were mutated by the DDarkside, and their red colouring might be an inherited Darkside mutation, and so would just get reinforced rather than altered.
However the Darkside corruption in agents and bountyhunters makes no sense, they have no force ability, so their being Evil would not induce any corruption.
Agreed. I wonder that about the non force using classes, maybe the idea is that the non-force using classes have some force sensitive abilities, which get backed up by Legacy Abilities. Just a thought.