Wow, I am so glad to see people actually getting some color into their lives! I'm an audiologist, and I tried to get permission to do my thesis on: "Why are HAs so Darn Ugly?" Because 50 years ago, they were huge, but stylin', and now...yeech!
So as an audiologist, let me comment:
Yes, almost every brand has color.
Siemens has translucent purple in some colors; I think Phonak does too.
Because cases are separate from the components, you may be able to convince your audiologist to order in a replacement case (not too pricey-maybe $100ish?) and just swap that. I'd do it for my patients. If you're under warranty, there should be little or no charge.
Typically, it adds nothing to the cost of a new hearing aid to get it in color.
I've never heard of glow-in-the-dark for hearing aids, though. And I work with a lot of brands. I like the idea, though.
Earmolds...wow, can we do funky stuff with earmolds. Severity of loss is not an issue: Westone, one of the most common manufacturers, can tint almost all of their materials, make glow-in-the-dark, can swirl multiple colors, and can add sparkles. This includes the silicone (what they call "feedback stoppers) and the acrylic.
IF YOU CHOOSE TO MODIFY YOURSELF: Be aware that this might do bad things to the warranty. I'd advise against nail polish as the solvents could affect the plastic, and if it leaked into the hearing aid would almost certainly screw it up. I'd also advise against fake tattoos: they're meant to be applied with water (you Rionet wearers can just stop looking smug) and they get sticky and gummy, which wouldn't really hurt your hearing aid but would look gross in a week or two.
Rub-on decals should work, just don't rub too hard, and stickers, beads, etc should be fine. Again, if you have an enterprising audiologist, they might be willing to art it up for you a bit. I used to do a lot of jewelry making: when I get to the point of needing a hearing aid, I intend to go with deep blue, with a few gems set in it and a silver dangle. I've got nice ears, and I don't see any reason why something I pay $1000+ for can't be pretty.
Anyone with questions can e-mail me. If you're in the Quad Cities area of Iowa/Illinois, I'm at Audiology Consultants (563-322-7333).