The intense green flame can be made with boric acid. If it's soluble enough in zippo fuel, you'll notice the flame color. Can't say for sure it's completely non-toxic, but there should be vanisingly small traces left after being burnt in a flame, that's used to light a smokable, that's puffed once, then the flame is extinguished. 'Tho I would chose boric acid, over copper salts for green color, just based on relative toxicity. I wouldn't use cobalt for blue. Or chromium salts at all. (what color does that make, I don;'t even know.) Strontium for red might be harmless, or not. But I'd go with lithium for red anyway, it's even found as a trace in mineral waters, even though it's a therapeautic drug, it is a little more ingestable.