ok here's the deal. I was going to paint you a couple of different techniques, but its exam time and the big one is on monday, so i've just done you my favorite:
base-coat the section to be painted in chaos black, followed by an ever so slightly watered down dark angels' green. before this last coat is totally dry you need to have yourself a 1:1 mix DA green and vile green. Dry-brush this on but remember to do it quickly whilst the green beneath is still wet. This provides adequate coverage whilst also allowing the paints to blend slightly and give an insubstantial flickering look. Slowly layer up with mixes that gradually tip the balance of colors away from DA and towards vile green, this should be done with a slightly moist brush with very little paint on it, but still move your brush like you were doing a very light dry-brush. After each coat applied in this way follow with a highlight of the same color. At any point during this process I recommend you apply a thin blue/black mix ink wash (2:1 respectively).
once you reach pure vile green, apply highlights on top in a mix of any bluish gray and vile green, gradually adding to this mix with space wolves grey. these should all be quite heavy highlights.
Finally, once you have done your top highlight of pure SW grey, water down some white paint (roughly 1:1) and apply like an ink wash to the lightest parts of the flame, this will appear to obliterate some fine work done previously, but when it dries, the undercoats should still be visible in all their glory, just with a ghostly white flicker. finally apply specific highlights of pure white, using a moist brush to blend in the edges.
my trial version (badly painted as I really am busy today and missing the blue/black ink wash as my inks sealed themselves shut centuries ago):
http://img167.imageshack.us/my.php?image=photo57th8.jpg
Never one for serious things, me
Well, cheers!
, but there will be others! You thought that was good? Then wait until I throw up the gag models I've made 
