I think the dragon expert is probably @TheEdVerse .

Ed, why doesn’t Tiamat have a single, unified rainbow breath? "Mixing the magic" inside her would cause an explosion = no more dragon head. As it's partly her breathing doing the mixing, every time she coughs or hiccups = no more dragon head…so Tiamat would be unlikely to survive for more than a few days after birth.#Realmslore

— Ed Greenwood (@TheEdVerse) September 26, 2019