Leucism is a condition that results when there is a problem with pigment metabolism in an animal. Sometimes it's called partial albinism, but a leucistic animal is not an albino--it does make pigment, just not 'normal' pigment.
This is a normal purple finch male after it's molted into its raspberry coloration in it's second spring (third year):
And these are shots of Mr Pink, our very leucistic purple finch. Notice that he has brown primary feathers on the wing--he's making some pigment, so he's not an albino. Also, the eyes are dark, not pink as they would be in an albino. I've heard that a male purple finch's raspberry coloration is partially due to what they eat, not something that they manufacture--so this bird is light because over most of its body it isn't making the proper amount of brown pigment, but is still sort of raspberry colored because some of that pigment comes from diet.
Isn't he cool?