Boric acid was added to a volumetric flask filled with a small amount of methanol, which formed the ester trimethyl borate. It's highly flammable and volatile, so it tends to form a clean flame. The boron atoms produce the greenish color.
If you want to try this at home, make sure to have the proper safety precautions: goggles, a fire extinguisher, and a safe method of ignition (don't use a lighter!) Methanol is available as HEET in most hardware stores; boric acid is used as a roach killer. Ironically, methanol is the more toxic of the two compounds. Swirl about 10 mL of methanol with 5 g of boric acid together (it will dissolve completely) and shake up the bottle to promote vaporization. Drop a match in and watch the thing explode.
If you don't want an explosion in a bottle, just pour the mix into a beaker or watch glass and ignite. You'll get a green flame. Excellent mood lighting for your chemical romance. I guess.
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Trimethyl borate is a boron triester consisting of a single boron atom bound to three methoxide...