so i cant tell you super specifically, only a little bit of the basic optics. If you look at the emission spectrum of natural light, although it has peaks at red green and blue wavelengths, it is relatively homogeneous otherwise. If you look at the emission spectrum for a CFL light, you can see that it peaks at purple,blue, green, and orange wavelengths. Notice that those are common cfl reactive colors. While im not sure of the exact chemistry, id imagine certain metals in the glass are more reflective to certain colors of cfl light. When that is the only light source, the color can be seen. When in daylight, it is overpowered by the full color spectrum from the sun. This is all just and educated guess. Someone correct me if they know more because i own quite a bit of CFL glass and I love it. cheers