In comparison to the other colored varieties, green peppers are often snubbed as being less desirable for our sophisticated palates. It is true they may taste different - which may or may not be desirable depending on the dish - but when it comes down to how much antioxidants they have, green peppers have almost the same total amount as the red, yellow, and orange sweet bell peppers.
ORAC Source
USDA Database for the Oxygen Radical Absorbance Capacity (ORAC) of Selected Foods, Release 2 - Prepared by Nutrient Data Laboratory, Beltsville Human Nutrition Research Center (BHNRC), Agricultural Research Service (ARS), U.S. Department of Agriculture (USDA) - May 2010