That doesn't look too bad in my opinion.
As far as I understand British tankers of the RAC during that time usually wore an overall over a shirt in summer and over the battledress in winter. The colors varied a little, but were mainly very close to the general infantry battle dress, I think. Some differences in insignia might occur, but as for color goes, I guess you can't get too wrong with using basic battledress colors:
https://www.militarymodelscene.com/lifecolor-british-uniform-colours?lightbox=dataItem-jbgrzud6And as I said: Your figure doesn't look off to me. Let's be honest: Finish them the way you started, place them, and then have a look at them. You won't be thinking "Something's wrong" is what I would probably bet on...
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