Thank you, @vkareh! I appreciate the further guidance.
Out of curiosity, I experimented by trying to replace the image for bar_unfocused.png with a darker substitute, to make my live window stand out more, but that didn't seem to take.
I used this
instead of this
I did the full rebuild after that change, but without impact.
I looked thru the build log and did not see any "reject" or "corruption" message related to that replacement file.
I even did a reboot to no avail.
Is there any reason why not?