http://macragge.oz.games-workshop.com/pain...ler/default.htm
Here you go. That is for Genestealers, but I'm sure you can work out how to do it for the Termagaunts. The Hawk Turquioise was painted onto the model with a technique called drybrushing, as described here:
http://macragge.oz.games-workshop.com/pain...ues/default.htm
Now, a word of advice. I'm just starting off myself and I began with the Space Marines paint set. Drybrushing will trash your brush. Don't use your normal brush for this. Buy a cheap one or use an old one you have.
You could also buy the Games Workshop brush pack. This includes a small drybrush, a standard brush and a detail brush.