The minerals that are used in the glass for color. Some minerals react to UV, fluorescent light or just the Kelvin temperature. This is based on the light and how the minerals reflect the light to your eye.
Basically, the light is white, with all colors. Then if you use say one kind of light source, it only has so many color wavelengths in it compared to the white light of the sun. Even white light is different based on the Kelvin temperature. Minerals.