Nice job, congratulation. About UCAC3, the catalog measurement where done in a single color, this is originally an astrometric catalog. The color information are merged afterward using other source of information for the published catalog. The data I keep for use with cartes du ciel are R and B from Supercosmos which come from Schmidt plate photograph. But as the globular cluster center are burned in this images there is no color information for this stars. You can observe the same near the bright stars.
Patrick
