One thing to keep in mind is that Unity8 was designed for the more “traditional” window layout: headerbars and client-side-decorations were not considered in the design afaik. As a result: the top bar of a window is the same color as the panel and dash because all three are “owned by the operating system”. They are not “part of the application”.
With Gnome3, headerbars and CSD, this isn’t true anymore: headerbars are “part of the application” so the style should match the application style more than the dash and dock style, like in the following two examples.
Files V22Nov17_LIGHT
V22Nov17_LIGHT_ROUND_SOLID
I think the first one is the best of the two because the headerbar is more clear, which will give users more confidence. (even with CSD, the headerbar still has distinct functionality; you can click and drag the application using the headerbar, but not using the rest of the application)