I think Mail is missing some coloring on the toolbar of the new Big Sur Mail app, which is obvious comparing it to other app windows. It's making the toolbar harder to view.
When looking at Finder, or Safari, when the app is in the foreground. The toolbar background grey has RGB 247,247,246. Finder has this same color when the toolbar is in the foreground. But Mail's toolbar is pure white, 255,255,255 when in the foreground.
When mail is in the background, the toolbar is showing the "background grey" 235, 234, 233 as do the other windows when they are in the background.
The pure white on the Mail toolbar makes it hard to distinguish since it blends into the white of the mail message background. It probably should be 247,247,246 as well.
When looking at Finder, or Safari, when the app is in the foreground. The toolbar background grey has RGB 247,247,246. Finder has this same color when the toolbar is in the foreground. But Mail's toolbar is pure white, 255,255,255 when in the foreground.
When mail is in the background, the toolbar is showing the "background grey" 235, 234, 233 as do the other windows when they are in the background.
The pure white on the Mail toolbar makes it hard to distinguish since it blends into the white of the mail message background. It probably should be 247,247,246 as well.
