At left is a juvenile White Ibis. The Little Blue Heron, at right, has all white plumage in its first year and dark blue thereafter. These young birds often mingle with Snowy Egrets; they actually catch more fish when in the presence of the Snowy Egret and also gain a measure of protection from predators when they mix into flocks of white herons. It is plausible that because of these advantages, they remain white for their first year.

http://en.wikipedia.org/wiki/Little_Blue_Heron