My small UV unit has "black light" tubes--but they look white when not turned on. When turned on, they give that classic black light glow to white cloth. In my large unit, I have BLB bulbs--"black light blue." When turned off, they are a deep blue/purple color. Both types of bulb will work. In fact, the white colored "black light" is a bit faster than the BLB. So, long story short, the color of your bulbs doesn't really tell you about the UV content of the light.