I just downloaded this browser for some of the visual advantages I see over Chrome. The main one that made me try it was the colored tabs. However, I wish that when you have the tabs on top, the entire top bar would be the tab color, like how it is when tabs are anywhere else. It'd be great to have an option for this as the white just isn't for me.
I asked for the same thing, having not only the tabs with accent color but the whole window with the accent color as well as the implementation of the fluent design.
It would be possible to mod this using a css mod. You might get help if you check out the modding forum.