In most skins, id="Controls.InputControl.Default" (and it's highlight, disabled, lowlight and modified brethren) is predominantly set to look good for the configuration panel.
Yet they dictate the colours for similar elements all over MusicBee, such as in e.g. the different tag editor panels. This is not ideal, but a compromise is usually doable for that. So this is not the foundation of this proposal.
But, since a related matter now came up, I thought to raise it anyway: An overrule for these for e.g. the tag editor panels could be useful.
But the primary issue here is this:
When you have set the colouring so that borders don't show where you don't need/want them, like this:
that will result in a problem for combo boxes where these borders blend with inputcontrol bg, making it impossible to see that/where you can click:
tag editor in sidepanel:
scan for new files:
I am not sure what the best solution would be, but I am guessing a new element for something like 'bdr in combobox' could be a candidate.