How to get colored flame from liquid fuel ?

Normally a coloured flame is achieved by putting a metal over a flame, for example you can get a green flame by putting some copper halide in the flame, or potassium will give a nice lilac flame.

This is caused by the present ions in the metal, which have their own absorptive and emissive spectra, giving this colour.

I have seen some lighters that use this method to produce different color flames.

I hope this is what you are looking for - please let me know if it isn't.

More info here (http://en.wikipedia.org/wiki/Flame_test).