A flat color CRT having a phosphor screen comprises red, green and, blue primary phosphor color stripes arranged at a spacing, and phosphor index stripes arranged in some of the spaces between the phosphor color stripes in a definite relation thereto. A black nonluminescent substance is provided between the phosphor index stripes and positioned at least in the spaces between the phosphor color stripes, and a metallic layer of sufficient thickness formed on the inner side of a tube panel and positioned in a corresponding relationship to the phosphor color stripes.