There was more than the obvious reason to feel blue for people offered in human sacrifice rituals by the ancient Maya to their rain god -- they were painted blue before being heaved into a watery sinkhole.

And it wasn't just any blue. It was Maya blue -- a vivid, somewhat turquoise-colored pigment used for about a millennium by Mesoamerican peoples to decorate pottery, figurines and murals that has long mystified scientists.

But now anthropologists from Wheaton College in Illinois and the Field Museum in Chicago have discovered how the ancient Maya produced this pigment and the role it played in important rituals at a famous Maya site in Mexico's Yucatan peninsula.