Hi Clint,
I had to play around with this a lot to figure it out but what I found was that you need to start with the built in high contrast white setting first as the template to change to your colors. That will give you the black title bar, if you don't you end up with purple or blue and possibly the white border you mention. Its not a perfect solution but it looks pretty good. I also noticed that the changes may not get applied fully until you restart or login/logout, I think windows may have to clear out the previous theme maybe. My display is 4k so your results may look a little different from my screen shots but shouldn't be much. Be sure to save the theme when you are done finding your color settings. The blue I used in the example is #49709C, the white is #E8E8E8, disabled text is #B3B3B3, button text #4F4F4F, background is #3D3D3D. Hope this helps.