My mistake... I was describing luminescence (electron jumps) but the examples were incandescent (thermal vibration of atoms). It's still the "cooling" that you see, whether it be excess energy from the atom or the electron.

http://library.thinkquest.org/27356/p_sources.htm

"exciting the electrons in those chemicals into a higher energy state. As they cool down, they move back to a lower state of energy, emitting light."

That's the explanation almost any time you see light, it's not unique to fireworks. It applies to any color of fireworks, regardless of whether the color is produced by the fuel itself or by the fuel heating another element. It also applies to candles, camp fires, butane lighters, acetylene torches, incandescent lights, red hot stove burners, halogen lights, etc.=.