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The plastic caps come standard with the sensors from GM's vendor, they are not spec'd to save GM money over other kinds or colors.
I had to change mine out for a HPDE that required metal caps with O-rings, so I got some black aluminum ones off eBay that I liked. I take them off to readjust the air pressure several times per year and have never had one that was difficult to remove with my fingers.
I tend to fine simple soap and water and use your hands (over a latex glove) as the cleaning tool works best.
The subtle mod looks nice. Granted my other ride isn't a Corvette I've done something similar with the caps. Went with titanium lug nuts with matching valve stem. Nice subtle touch for the wheels. I can take a better photo later but just went snooping around my albums for a quick shot to show...