Zen!

The zen-ful question has been partially addressed! After talking to an enthousiastic photographer, it appears that the Snowy Egret uses it's yellow toes as 'bait' to attract minnows.

This doesn't mean that this was the original reason yellow feet evolved, but it's a step in the right direction.

Questions remaining:

1. Immature snowy egrets have yellowish-greenish legs, they don't get totally black until adult-hood ==> Yellow feet/black leg combo related to mating?
Note: Another egret, the Cattle Egret, has yellow/pink legs in the breeding season and dark legs in the winter

2. Other Egrets, such as the Great Egret, have dark legs

3. And why are all these tropical wading birds (Great, Cattle and Snowy Egrets, White Ibis...) white? Even the Little Blue Heron immatures are white and some of the big Herons (Great Blue Heron and Reddish Egret) have white morphs. What's with this colour?