Yes. Only clear is 33 COE. Minerals are added to the glass to get it to change color. When this happens the properties of the glass change. This is part of the art of glass. The blower must know how the color will work. Also, the blower must also know what kind of flame atmosphere to use when working the color so it is not destroyed.
For instance Jet Black is one of the densest and hardest to get to melt. If it is next to clear more heat has to be applied to the black to get it to flow like the clear. Also, black can only be worked in an oxidizing flame or it
Some colors also need to sit in the kiln at a high temperature. This can be to get the glass to strike, or to get the glass to be even so to speak.