Then there is the condition called vitiligo which could be considered a type
of dermal variegation for humans.

As I explained already, vitiligo is not the human equivalent of variegated
foliage. The white patches in vitiligo are the absence of melanin pigment. The
entire skin has a blood supply, otherwise gangrene would occur.
Vitiligo can be compared to a plant which has patches of red or purple on green
leaves, like some coleus, not on white and green variegation.
In variegated foliage, the venetion throughout the leaf is normal. The palisade
layer, which contains the chloroplasts, is missing, or some of the chloroplasts
are lacking in chlorophyll. The green parts of the leaf perform photosynthesis
and send nutrients to the white part. But this is similar to supporting
flowers, so variegated plants tend to be weaker or slower growing than all
green ones.
Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)