Minerals are used to color glass. Many times he minerals and ratio of the minerals in the glass are considered a trade secret to the manufacturer of the colored glass. Here are a few examples of what minerals help the clear glass turn color.
Cobalt Oxide: blue-violet
Cadmium Sulfide: yellow
Gold Chloride: red
Antimony Oxide: white
Uranium Oxide: fluorescent yellow, green
Chromic Oxide: emerald green
Note, when any mineral is added to the glass it does change it COE (coefficient of expansion). While the clear glass claims a COE of 33 the colored glass will also claim a COE 33. But this is not true that they are the same COE33. They are close but not the exact same.