Windows 10 Limitation
I agree that the current Win 10 dark theme is not complete, even in their own pop-up alerts the default color selected in personalization comes through. So, there are elements of the Win UI that are not fully adopting the dark theme.
Supposedly, in Win 10 1903 (April 2019 update), dark theme is supposed to be improved. Of course, installing a Win 10 feature update like 1903 is always tricky, as early bugs are often reported. I wait a solid month before updating.
Even though there are still elements that are not dark, the new theme in WinSCP is much appreciated and will certainly work for now.
Supposedly, in Win 10 1903 (April 2019 update), dark theme is supposed to be improved. Of course, installing a Win 10 feature update like 1903 is always tricky, as early bugs are often reported. I wait a solid month before updating.
Even though there are still elements that are not dark, the new theme in WinSCP is much appreciated and will certainly work for now.