Archie and I have discussed this before. The same thing happens in London. Light blue is always in use and difficult to get. The stacks nearest the house chips may be reserved for highe denomination play, and if they are used for regular play as there are no colors left, they will normally count the stacks out under the camera before they give them out. As London has machines that sort the chips, they know within seconds of the spin if they are short. You have to leave fast. It also means you can only obtain one 'difficult' color per visit to the casino.