Why do some glass colors cost more than other colors.

There are many factors to this.

1. Origin of the color plays a large roll.  Glass made in America costs more than glass made in China due to labor and material costs
2. Minerals used in the color play a very big roll.  Gold is not cheap
3. The batch size plays a large roll also.  The more they make it, the cheaper it can be made.  So new colors are more expensive as it takes a new crucible just for that new color.