what colour do u think i should paint my plague marines

and also will citadel spray paint work on metal models so that i can paint ova the undacoat?

The traditional Nurgle colours of Kommando Khaki and Catachan Green come to mind.

Citadel spraypaint works but I still prefer to do it by hand if there is only a handful of models to be done at a time.

I would suggest a goblin green base coat with a light green and brown wash. then dry brush with a mix of cammo green and bleached bone. Also try a technique called splattering. Take a larger stiffer brush and mix up a darker ink of the greenish brown, ading some chestnut wash would work. What you do is load up the brush and using your thumb pull back on the bristles like the hammer of a revolver and let the paint splatter allover the model. Its best to do this after all the armor has been painted to your likeing, make it your last step. Be sure to experiment on an old model or peice of sprue to get the look your looking for. Good luck!

Well there a variety of ways to paint Death Guard,depending on how unique you want them to look and what look you want for them.
But anyway i thought you would love to see this: http://www.jeanfrancois.org/web/articles/articles_dgpainting.html
Its a great tutorial on how to paint plague marines and it should help you out tremendously.
Cheers,
Tycho

i looked through my old coppys of white dwarf and found a few articles that may be of some help to you. w.d. # 282, pg. 74 has the article on the splatering method, this article is on Andy Hoaers's nurgle plague marines. also w.d. #289 pg.110 has an article on Tammy Haye's nurgle chaos lord, typhus. both articles are verry good and i recomend them highly,
good luck!