I'm thinking about any color could throw things off kilter to some degree. My skin/makeup (and I don't wear much, it bugs me) can look fine in my bath (gray based mid level purple). If I then leave and go to my sister's, who has a beige with a subtle pink undertone and regular bulbs, my skin looks ashen in her bath. Yellow based beiges can make skin look, well, yellow. ;) I'd focus on lighting, as SQH mentions. I use either Full Spectrum bulbs or GE Reveal, not only in bathroom but throughout the house. It makes a huge difference (and I find it much cheerier). If you're skeptical grab a package of GE Reveal (I've found Target has them priced well) and give it a try with your current color and note the overall difference in the room. Full Spectrum are much more costly (about $7/bulb) but they have lasted several years for me in one fixture. I've had this older photo kicking around, and have posted before, but will offer again in case you haven't seen it. These are family room walls, back when they were just a creamy, slightly off white. Taken with no flash in both cases, only light was from lamp. Regular bulb: Full spectrum bulb:

Are the fixtures you want to use Moen? I would find out if the valves are interchangeable between Moen fixtures. If just swapping the trims won't work, changing valves out after the fact will require wall surgery and pipe cutting and soldering as they are soldered into place during the rough-in. If the showers are tiled you're talking major surgery unless you can get to them from behind. I agree that it's probably going to cost you more in the long run to do it this way.

Who will be using that bathroom? My oldest took baths exclusively until he was six. My youngest is still taking only baths at five. So ideally, I'd have a tub in bathrooms used by kids. I know you said your kids are gone, but do you have visitors with kids or grandkids now or potentially soon? For resale, if I had kids and was looking to buy I'd prefer a house with a tub in the bathroom used by the kids, rather than storing their toys in my bathroom and having them troup into my bathroom. Same with a guest bathroom, it would be nicer to have the ability to bath my kids and I would definitely not want to impose on my host to use the master bathroom. On the other hand, if the bathroom will be used primarily by elderly visitors, a walk in shower would probably be better. This is very much guessing, but I'd think cost is probably a wash? The tub will be more expensive in materials but cheaper in labor. If you go with the inexpensive kohler cast iron tub available at Home Depot, you are probably ahead of a tiled shower floor in cost? The tub is definitely cheaper than a cast iron shower base.

The only way to answer your question is to see the cavity behind the trim plate. specifically how its vaporproofed and then see that all the residue was removed from caulk properly allowing silicone replacement to bond correctly and not trap caulk residue. The vaporproofing should be tied in behind trim as to not rely on an outer bead of silicone and in so trusting that trim kit itself wont allow vapor to pass into wall cavity . It would take an onsite asessment to verify A >Good to go.:)