they are more dark green if they a understory plant, or a shaded plant. there of course plants that have no chlorophyll whatsoever. 2 types, one is mostly albino plants where they lose all thier chlorophyll, the other is mycoheterotrophic plants(either partial or fully). ever seen a albino redwood, apparently it lives off being attached to the roots of the parent plant where it came from or from nearby trees.

I know this is a joke, but to be fair: the scientific consensus (now) is that the purple pigmentation acts as a sort of sunscreen against too much sunlight.