Those paint jobs look good! It is hard to get great results- I sometimes use a spray paint to avoid brush strokes, but it is hard not to over-spray and get runs. I found I had to use a plastic primer undercoat to get the paint to stick to ABS plastic.
Another alternative I have been playing with recently is to use digital photo-manipulation to change the colour of PM parts.That way, no PM parts are harmed in the filming process!
I am no adept, but having Photoshop Elements on my laptop (which I got a few years ago in a software bundle with a new camera, I think) I played around with the Quick Selection Tool and the Smart Brush Tool. Here are a few results. PS shows the photoshopped part (in case you can't tell!)
Before
After
Before
After
Before
After
Before
After
I think the white waistcoat is the best of the ones above.
And when short of a part, Photoshop can help too:
Which of the helmets is the original and which a PS copy?