We identified a single mouse with a greyish-tan coat color and ruby red eyes in one of our C57BL/6J-derived congenic lines for the ozone project. The substituted A/J-derived congenic region was eliminated and the color coat regenerated, demonstrating that the mutation was not in the congenic interval. This color coat mutation is now on a pure C57BL/6J background. We are now generating an F2 population with A/J mice to map the trait and determine whether this is worthy of further analysis. The F2 population has at least 6 different coat colors, rather than the expected 3 coat colors from a typical cross of A/J and C57BL/6J strains (i.e., black, white and brown).