Mixing colors of glass cullet can have more serious effects than just off-spec colors. In small amounts, the bubbles show up in the walls of the finished bottles and jars. This not only detracts from the appearance of the glass, it may also weaken the container walls and lead to breakage. Green glass is the most forgiving in its ability to absorb other colors. Amber is slightly less forgiving.
Clear glass is the most easily contaminated by other colors.
For this reason, a load of contaminant free clear glass sells for the highest price, while mixed glass may have no value at all. Some markets only accept mixed glass from sources who also provide clear or color-sorted glass. Occasionally markets may not accept mixed glass at all. Blue glass, a recent addition to the list of glass colors, may or may not be accepted by end markets. Those markets that do accept it generally specify that it be blended into large quantities of green or amber glass.