Sometimes different qualities of white are available at the plant to be used as the base glass.
I can only speak for the Jabo Joker team. We choose the color we will use and we bring it with us, or arrange to have it shipped from outside sources, to the plant. Over the three years, we have used a few different base colors.
We purchase base glass and a wide range of striking (colors) glass from outside sources for each run.
Each investor group differs in their approach to the process.