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Have you considered accessibility support for color blindness (of the most common type)? Since the theme tries to maintain a constant contrast (of 7:1 between the fg to bg), all the various colors probably "look" the too similar to someone who do not perceive the colors as distinctly as trichromats. On the other hand, if a theme varied the contrast rigorously (like one of those monochromatic themes), then that would be helpful for any type of color blindness.

I am not suggesting this theme should be color-blindness friendly; not my call and I am glad as it is. I am simply wondering if that is something technically feasible for the "most common types" [0]. If feasible, is that possible to achieve that with minor tweaks without creating a completely different modus variant?

While anomalous trichromat don't perceive the the colors exactly the same as trichromats, they can still distinguish them well, and difference in sticking color names to wavelengths isn't too important for a theme. Monochromats are rare, and as the name suggests, they probably prefer a monochromatic theme anyways. Therefore, it should suffice for a theme trying to be color-blind friendly to consider the following "most common types" of dichromats:

• Protanopia (1% of males), reduced sensitivity to red-green
• Deuteranopia (1% of males), reduced sensitivity to red-green
• Tritanopia (less than 1% of males and females), reduced sensitivity to blue-yellow

To asses if a color theme is color blind friendly, one can check the colors used in the theme against the dichromatic isochromatic/confusion lines [1,2,3], and try to make sure they (or at least most of the colors used in a theme) do not fall on the isochromtatic lines.

[0] https://en.wikipedia.org/wiki/Color_blindness#Classification
[1] https://www.cs.cornell.edu/boom/2004sp/ProjectArch/DaltonsJungle/daltons_jungle.htm, Figure 2
[2] http://www.ahpo.net/assets/CET%20C-11998.pdf, Figure 4
[3] https://www.color-blindness.com/2007/01/23/confusion-lines-of-the-cie-1931-color-space/