Why do I often have blue feet?

Why do blue-footed boobies have blue feet?

• Stephen J. Gould wrote a book called The Flamingo's Smile that explained (among other things) why flamingoes eat the way they do and have the color that they have: it's due to the shrimp that they eat. Wikipedia explains that the blue of the blue-footed boobies feet is due to their diet, but it does not specifically say what in their diet causes the blue.  I'm looking for scientific answers, not "I'm an idiot" answers provoked by the use of the word "booby," tempting as it may be.

• Answer:

  Blue-footed boobies produce the blue foot pigment from carotenoids found in anchovies, mackerel, and sardines. It is thought that zeaxanthin is the main carotenoid used to pigment booby feet, but carotenoid metabolism by birds is not completely understood, and it is possible other carotenoids are used as pigment as well. Other carotenoids found in blue footed booby blood plasma are lutein and canthaxanthin, as well as smaller doses of not-yet-identified carotenoids. Source: Morales, Judith, Alberto Velando, and Roxana Torres. "Fecundity compromises attractiveness when pigments are scarce." Behavioral Ecology 20.1 (2009): 117-123.