A small intro, as it is a subject I have read a lot about.
Stug crew was not considered panzer crew (SP Artillery), so they wore feldgrau with red artillery pippings. That would be the norm. There were (as always) exceptions, Lehr Stugs is one that springs to mind. So anything from panzer jackets with red pipping to black panzer jackets with pink pip pings can be correct.
For a regular Heer StugBatterie, feldgrau with red pipping would be correct.
That said, go for Vallejo Model Colour Feldgrau. Can't miss there. Vallejo Panzer Aces should also have something similarly named.
PS.: I'm failing all my Willpower saves vs. Warlord's new Stug with Maelstrom's 17,5% discount... 
Thank you for your small history lesson, even though it had nothing to do with my question. Besides, you are not totally correct, but its a confusing matter for most, so that is quite understandable and hence can be excused. I can give an exampel, Panzerjäger or Stugs within a panzer regiment of a panzerdivision, ersatz units etc ;-)
I am fully aware of who used what uniform type, along with piping and their colours, Epaulette and Kragenspiegel etc. It is the names of the colours I need!

Perhaps I must re-phrase my question to make it more clear. What I would love is a suggestion for what colour to use, preferably from the Vallejo range, to paint the SP uniform (once again, its name is best translated to the Special Motor Uniform, but in this case, the grey and reed-green summer version). Primarely I am looking for suggestions for the Reed-Green Summer version of the uniform. The normal grey I could use a lighter version of the field grey I am sure.
By the way, what new Stug would that be?

You really cant tell me stuff like that, I just made so many orders that my credit card is burning!!!
I suppose I must check it out... Maelstroms you say eh?
I have one Warlord Stug, but I think I will continue to order from Die Waffenkammer, they just have too many cool veichles, besides, the owner is a very polite and nice guy.