"Anthocyanins play a very versatile role in pollination, especially in the Bromeliaceae. Certain bromeliads turn a vivid red just before and during pollination but soon revert to the original green color characteristic of the photosynthesis pigment, chlorophyll. Anthocyanins are not a biochemical dead end but rather a dynamic signalling device that can be switched on when needed by the plant to assist in pollination. They are then degraded by plant enzymes when no longer needed to attract pollinators to flowers."

From http://www.charlies-web.com/specialtopics/anthocyanin.html