Despite my original reservations I really really like Titans Return Sentinal Prime. Don't do a whole lot of reading IDW, so his comic representation had no real pull for me. Thing is, for everyone who doesn't like his color scheme it works for me in two big ways. 1 - Orange is my favorite color & 2 - his color scheme reminds me of Rodimus/Hot Rod which is another plus. A great figure overall (so much so I can't even see Astrotrain in him), but as many have said he's lacking in paint apps, which really hurts both of his alt modes. So inspired by so many others, I tried my hand at a few paint apps of my own.  
Not much for his headmaster, but I added a couple of touches of silver to make it look a bit better.

For the shuttle mode, the biggest weakness in my opinion was that the windows were the same color as everything else. Fixed that and added a little silver trim to the wings and fins. A bit of silver and gold here and there (not too much) and I think it looks much better.


Here was the mode I felt needed paint the most. I actually like the funky "space-battleship-war train" mode. Its kind of weird, but in a good way. Problem was there was so little paint, this mode really didn't look like much to me. Touched up the wheels and painted some of the windows. I'm pleased with the results.


No major changes to robot mode outside of the touch-ups visible from vehicle modes. Did add two spots of silver on his abdomen, and then two more on his "belt". I did paint the tip of his gun silver as well because it looks better than the orange tip. I had considered adding a bit of silver to his head, but I like the "all orange" look for his helmet for some reason. You'll notice that his feet are asymmetrical. I like the idea of the "front" and "back" of the train being separate feet. I set it up so the "painted" front folds in, and the "unpainted" one is visible in robot mode.


So there you have it. The touch ups have moved him to the top of my Titan Returns favorites ahead of Chromedome (2nd favorite) and Weirdwolf (3rd favorite). The apps aren't as extreme as some I've seen, but I wasn't trying to give him a new paint job, just wanted to do enough so the lack of paint apps didn't take away from the figure as a whole. Opinions are certainly welcome!

 

I share your approach to painting. I don't like my Transformers to look like they've been customized, so they usually just get the paint that Hasbro left off. I love the gold windows in particular, and I think you did an excellent job making that weird jagged foot look like it may actually be the front of a train.