Well they use color inducing chemicals apparently, in military smoke grenades, that have a variety of colors. So that stuff might work whatever it is, to add to the charge. But it sounds like maybe a blank slate experiment if you cannot find someone who has done it before. Maybe colored confetti? Or talk to fireworks folks like the link above? I would think the cannon maker would have recommended charges and I would stick to that, like they said, one bad boom and cannons will be banned in your county!
Your gun is like your nose, it is just wrong for someone else to pick it for you!