I know this is going to sound crazy on my part but I think you'll find that it's a simple case of what "looked good" under 16bit won't "look good" under 24bit. Let's see if I can explain this:
You've started at a lower resolution and turned it up, so now it's become "fuzzy" and hence there are "spots" showing through. Something like a skin should be made at a
higher resolution and that way it can be seen just as well at a lower resolution/bit colour just fine, not in reverse.
Now I could be all wet behind the ears---but I've noticed that when I've made things at 32bit and have scaled
down I've never had a problem (I'm a themer by the way, digital artist, and I dabble in screensavers). However, when I've done what you've done
sometimes---not always---I've encountered the exact same problem which required that I started over from scratch at the higher bit colour.
Talk about a pain!
But when we make shell themes this is why we start with the highest resolution first and work our way backwards.
I hope this helped a little. This has just been my experience. User mileage may vary.
À la prochaine,
Eyes-Only
"L'Peau-Rouge"