Thanks Greg, I was wondering why my attempts at inserting an image were mis-behaving.
Actually, Transparency was checked, but grayed out. "Increase contrast" above it was checked however. When I uncheck "increase contrast" it does make the brown highlighting orange, (my selected color now is Yellow) but the rest of the interface tends to have whiter lines around window frames rather than black, making it more difficult to read the screen.
I also spent some time in the color panel to select a different Color Display Profile from among the couple dozen I have. I did find one that was the least-worst, and am now using that; although it has no real affect on the concerns I noted above. I also tried adjusting the monitor's built-in contrast and sharpness to no avail. I still believe the difference I'm seeing is not in the color profile but rather some distinct aspect of Xojo; but welcome all suggestions of things to try.