I got bored with playing around with the test mini, so I started applying the colour scheme to the rest of the Marines. Yup, seems to work. The additional minis seem to get a bit whiter than their testmini comrade, but once some more colours are added the white won't look quite as white any more and will just give a nice contrast to the darker parts.
And if there's still something looking too 'nice' - just apply some icky looking effect here and there. Nurgle is all about fun. In moderation, otherwise you end up with a sticky mess. Rules are good. They help control the fun. :-P