Why are robins' eggs so blue?

Question

http://images.google.com/images?um=1&tab=wi&q=robin%27s%20eggs

Answer 1

Robin eggs are blue because they belong to the thrush family--many thrushes (including bluebirds) lay blue eggs. Other birds that lay blue or greenish blue eggs are starlings, cormorants, and herons. Most birds with open nests lay eggs that have some color, which makes them harder for predators to spot than pure white eggs would be.

The egg shell color comes from pigments in the mother robin's blood! Hemoglobin from ruptured blood cells is transformed into "bile pigments," which are carried by the robin's blood to where the eggshell forms near her "cloaca."

Answer 2

If you mean, why blue and not some other color, here is ONE viewpoint:

"...how do scientists explain the fact that robin's eggs are an eye-catching, unmarked blue? Perhaps this enables robins to spot when a parasitic bird tries to add its own eggs to the nest. For some species, this may pose a greater threat than that of nest robbers."

http://amos.indiana.edu/library/scripts/eggcolor.html