@ICIT2LOL: Thanks, and don't worry about the delay; I've seen much longer ones in forum discussions.
This is actually the way my icons were treated even when the computer was brand-new right out of the box and I hadn't installed any 3rd-party software yet, so I doubt if there's anything out of whack in the system files. Since my Windows 7 version is the Starter Edition, I have no access to themes other than Windows Basic, Windows Classic -- which I'm using now -- and a couple of high-contrast color schemes. My partner's machine is running Windows 7 Home Premium. His desktop icons behave differently, but then he's not using the Classic color scheme, but I don't want to switch to that on his system just for comparison's sake.
What I have noticed is that icons in the Windows Explorer file lists don't get dimmed when selected, only the desktop icons. In XYplorer, which I also use for file management, there's a setting to disallow dimming of selected icons in the lists, and the help file explains that dimming them was the default in Win XP, but not in Vista or Win 7.
Anyway, I'm quite proficient in tweaking the registry, which I've done for a lot of other Windows 7 features (aka deficiencies) without causing problems, but if there is no obvious key or value that applies in this case, I won't pursue the matter any further.