I thought the tab close button highlight was based on contrasting with the tab close glyph and/or tab background color, but it looks like incognito state is being taken into account in a strange way; see attached screenshot.

In normal windows, my close button highlight ring against the tab background is #e8eaed on #1f841f, for a contrast ratio of 3.97.

In incognito windows, I get #5f6368 on #157217, a contrast ratio of 1 (!).

We should probably use very similar colors in these two cases, since the tab text and background colors are similar.  And we should ensure the contrast ratio is sufficiently high -- IMO the highlight should probably hit at least 4.5 against the tab background given the potential for dataloss from accidental closure, so even the normal window here isn't quite good enough.
 

Deleted: contrast.png 5.0 KB

	contrast.png 5.0 KB View Download