When it's not the active window, the tab bar is an even lighter gray, and the font color on inactive tabs is still white:

So my primary complaint is that in Opera 50.0 the inactive tabs use a white font that is nearly impossible to read against a light gray background.

But I also think the top bar of the window, including the tabs (at least the inactive ones), should be a dark color, instead of nearly the same light gray as the regular browser. It would make it a lot easier to distinguish the normal browser window from a private browser window.

Also the private url bar is now a very stark black background with white font. Too much contrast. A medium dark would be easier on the eyes.

I think the visual design of private/incognito browsers is much better in Firefox and Chrome, where the entire top bar of the window is dark. The active private tab is a lighter color. There is appropriate contrast between the private tab and its font, whether active or inactive tab, so you can read it.

FF57 Private:

Chrome 63 Incognito:

Thanks for reading.