I work for a model train company, and I've been doing the renders of upcoming products for our print and video advertising. I'm just getting my feet wet with Blender, but I've learned a fair amount over the past several months.
So far, I've been generating these plain renders without any artwork, just changing minor things like making the windows transparent and the wheels metallic. I'm fairly happy with how they look, but I want to take my game up a notch and "paint" them with the colours and logos that will be on the production models (see attached).
I've messed around with texture and vertex painting, both of which are convoluted messes for something that seems as though it should be relatively simple. For example, I'll paint the faces at the rear of the engine red like in the artwork, but then I'll also get random red blotches throughout the rest of the model.
Is there a straightforward manner in which to do this that I might be overlooking? For reference, I'm using STP files from our factory (imported with the STEPper plugin) and I'm on Blender 2.93.
Thanks in advance!
Postscript: Your answer was profoundly helpful and I can't thank you enough. While it was a bit tedious, particularly the gaskets around the windows, it was fairly straightforward and the painting is mostly done. I'll tackle the logos and stripes next. Thanks again!