That is something I can't explain, but it does. Your grey__dark blue__and red chalks produce the better sounds out of a call. They are all made by the same company and the courseness of the chalk powder is the same, but the color makes a difference, no clue why? There is a difference between a railroad chalk and a carpenters chalk, as in how fine of grit the chalk is ground into. Even in those certain colors play better that other colors do? Some calls prefer a finer grit chalk and some a courser grit?