I'd love to use the "Extra quality levels" option, but I'm currently only setting it to 1 additional level past the 3 you normally add, just because every level after 8 is the same black circles icon, making it impossible to tell the really high qualities apart at a glance anymore.

Would it be possible for you to include additional custom icons for the optional extra levels? At least some amount of them?

So I wouldn't make custom icons for each. One approach could be to generate different colour patterns for each, which I'm not completely opposed to.

The design reason for not doing this is that I didn't think it would add much benefit. At that level of quality things are very likely going to be automated and telling the levels of individual items apart just by the icons is unlikely in my mind, and the order isn't easily remembered. It's the same reason I left the names as x8-x99, instead of having to recall that Spectacular quality is after Impressive or whatever.

All that to say, not immediately, but I may incorporate it in a future release.

Yeah. Take Infinite Quality Tiers as an example. Great little mod with 250 fucking qualities, but most of the icons are randomly colored. lol

Looking at that in a large base, you wouldn't be able to tell what quality something is. It could be anything.
In fact, I just did the math. For 5 pips and 3 colors (red, green, blue), there are about 3^5 possible combinations for the icons

I was just playing in Krita and thought of an approach:

Color the center of each pip of the x8 icon, in sequence, one color (red, green, or blue). It starts with one pip being colored green, the top-left one, then both top-left and top-right both green, and so on, incrementally coloring all the pips, leaving the center for last. Then, clear the colors back to the original x8, and color each pip the next color (red), with the same process as for green. The order of the colors can be in Factorio-style (GRB).

PS. Maybe instead of starting with green, the first color can be white, then GRB, then black.