One Flash, Two Colors
I probably would have chosen to use a different set of colors than he did in his example shot - cool gel on the background portion and warm on the hair portion would be my choice. But the technique is pretty nifty.
If doing this with a speedlight, you'd need to make it into a quasi-bare-bulb light first. Use a Sto-Fen Omnibounce, or just a small Tupperware container.
:: More detailed bare-bulb info ::
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