Steve,
After looking at the photo and additional clues you sent me, it
looks like you're seeing the effects of unsuccessful dithering.
What I mean by that is that it appears that the video bandwidth of
your "100" is a little greater than mine, thus the alternatingly
colored blue bars of your desktop are individually visible rather than
being smeared (dithered) together to mix into a 3rd shade as they
would be in a lower bandwidth monitor.
If the bandwidth was WAY too high, then you'd also be seeing the
"poster child" aliasing effects that Michael talks about, and which
I've experienced with a variety of other attempted IIgs->VGA methods
described way back in this groups archive.
What this might tell us is that either they changed the filter
design of the 100 slightly (since it's been several years since I
bought mine from them), or that your unit is either out of or just
further out of spec or adjustment.
Contact their tech support via email and ask if there's been a
design change with it. I think the guy's name was Steve also -- I
can't remember.
Another option would be to mail me just the base unit and have me
swap in for mine to verify the problem. If it doesn't perform the
same as mine, I'd explain the problem to Steve(?) and return it.
There's other viable options.