Very cool "leucistic" Atlantic Puffin, photographs here, tip given on the 10000 birds blog.
Time to revisit a rant... Leucistic is a useless term. The article states this bird is diluted. It's not, look at the dark spots. It's got large white areas. Another tipoff is the small dark areas on the rest of the body - a dilute will either be diluted overall, or will have one color diluted.
The difference is clear to see, and the photo doesn't fit the description - looks more like the pigment is absent in most places, not that it's diluted.
Read my full-on rant here.