I appreciate that this is a peculiar request, but other than prismatic belts, nobody has really done a mod that makes the belt color the most prominent feature of the belts. I know that the thick stripe option exists, but is it possible for this mod to have a config option that makes the arrows black, and the rubber take on the belt colour...?

Now THAT's an interesting idea. But could you tell me more about it?

If I understand you correctly, you'd like an inverted version of the "thick line" arrow style?
As in, the middle stripe is rubbery black while the sides of the belt are colored...?

The way the mod works is by overlaying a mask (colored based on the belt's tier) over the arrowless black belt sprite. "Inverting" existing arrow options isn't really doable without a lot of effort to remake each sprite (or force the game to do it automatically, which I'm not sure is feasible).

I could try to make some custom graphics for a few cases though, such as an "inverted thick stripe" style.
(Or alternatively add an extra tinted mask between the base and arrows to have a similar effect to the prismatic belt mod.)

I would like an inverted version of the base-game "vanilla" style, actually - but the idea you've proposed also sounds interesting.

That said, the limitations you've explained make sense enough; I wouldn't want to propose something that takes an excess of effort, so I am perfectly fine with this ticket being marked as "Dismissed." I had envisaged it as being an inverted (or perhaps brightened?) mask of the rubber-belt-base-*.png files with the rails and rollers removed, and the original arrow graphics erased from the resulting edited sheets. It might be possible to do this in an image editor with just masking and filters, but having looked at the graphics files inside the mod, I can see now just how much time that would take...!

I could possibly take a bit of time to see if I can tinker with the graphics and report back with results, but even though the mod is released under MIT I'd think it best to ask your permission in case the task overall isn't one you're looking to tackle right now.

Feel free to try stuff out, if your spritework is good enough I might implement it to the mod. (otherwise, you could always code your ideas as a separate mod...?)
I might try to add the "side stripes" option I mentioned, because maybe someone would like that.

I'll see how a "prismatic belt" mask and option would look like, and might implement it, although I don't really want to replace prismatic belts itself. Unlike belt glow (which is just one extra line of code in BRB) and arrowless belts (which is already built in BRB's spriting logic), prismatic belts is a bit more unique.