Older eyes can not see the sidebar items on a black background, especially when the letters are subtle colors, or not pure bright white. We need an option to lighten the background, or at least increase the contrast to make letters legible and viewable. I may have to go back to Apple Mail app if this doesn’t change.

Please ask the 20 somethings working on the UI to test it on their grandparents, parents or even their older colleagues.

Will never be my default client on either OS X or iOS until the sidebar is readable.

I may have added my comment for the desktop version, this is even more important in iPhone and even iPad. Just add white, doesn't have to be fancy!

I'm on an ipad pro and i can hardly see those little fonts, I don't think I'll even install on my phone. Please permit a white background, and bigger fonts.