Post-harvest darkening of seed coat color is a major problem to all market classes of dry bean (Phaseolus vulgaris L.). Darkened dry bean is less attractive to buyer and consumer and is heavily discounted in the commerce. Our objective was to develop slow darkening pinto bean for the U.S. markets. Two breeding strategies were used: white-seeded great northern ‘Matterhorn’ was used in one cross and a slow darkening tropical pinto bean germplasm accession G 17341 was used in another cross. Because slow darkening is a recessive trait affected by environment, its frequency was extremely low, especially in early generations. Large populations and multi-location testing in drought-stressed, low soil fertility, and continual bean cropping environments were used for development of one stable slow darkening pinto bean breeding line from each population.