RFE: E-Ink theme

The extant RedReader themes are not suitable for E-Ink devices. Many buttons are unable to be read in any theme, among other smaller issues. May I suggest that an 8-level greyscale theme be added to RedReader?

I did try the OLED focused Ultra Black theme, but I found it unsuitable for E-Ink devices for the following reasons:

1. The background is black. E-Ink devices work best with a light background and dark foreground.
2. Many buttons and menus are not visible. As an example, in Settings -> Appearance -> Theme I can not actually see anything inside the dialogue box that pops up. This is the case with all themes, not just Ultra Black.
3. After updating I had to accept the new Reddit terms. But the buttons in the RedReader UI were completely invisible in all themes.
4. When submitting a comment, the popup just looks blank. I suppose something is written there, but I can not see it. All themes.
5. When long pressing a comment, the context menu is the same colour as the background and has no border. It is very difficult to make out the boundaries of this context menu. All themes.

I expect that there are other problems that I do not know about, simply because I cannot see them!

I am using RedReader version 1.23.1, to which I upgraded from whatever was current in February 2023. That February 2023 version has these same issues, I upgraded specifically to see if things had gotten better.

Start by reproducing the reported problems on an E-Ink device using the existing themes, especially Ultra Black, and inspect the Settings → Appearance → Theme dialog, comment submission popup, and long-press context menu. Review how the current themes define backgrounds, foregrounds, buttons, menus, and borders. Done means an added 8-level greyscale theme makes these UI elements visibly distinguishable on E-Ink while preserving the existing theme choices.