First, thanks for your post.
Bold gray line at tab bar dosn't look great.
I'm aware of that. To be honest, it has a low priority as it looks like that only if you have visual themes turned off in Windows.
I've found strange white background in file properties dialog. And strange file path label colors:
White background: will take a look.
Path label: Fixed. https://winscp.net/tracker/show_bug.cgi?id=990
Same strange colors are in progress dialog:
The same. Fixed.
When I move mouse pointer over path components at inactive panel, they are become same color as background. Previous version doesn't have this glitch.
Path components at active panel have same colors as before but also look awful.
This is taken from your (non-standard theme-less) Windows color settings (Active title bar and Inactive title bar colors).
It do not think there was any change since the last version.
I admit the selection of hottrack color is not ideal (Though still, in most themes, it won't be the same as background color). I'll take a look at this.