When I first started seeing this pure white House Finch at the back yard feeder, I wasn't able to see the eye color. If it's pink or red, then this would be an albino bird, but normal brown eyes indicate it's leucistic.
Albinism causes an absence of melanin, which colors the skin, feathers and eyes. Leucism causes only a partial loss of pigmentation where the eyes are not affected. An albinistic bird has pink eyes resulting from the lack of pigmentation in the eye. The color comes only from the blood vessels in the eye. This completely white bird still has melanin because the eyes are dark.