Tried some new dirt tiles to reduce noise. A couple of varaiations red and grey and adding red to brown and grey, with grey and black backgrounds. Given the questionable nature of the magenta I dropped it and resigned myself to using black edging against the gray.
I quite like the bottom grey on red except on the underside where the red just looks too luminous.

I think the black as bg is inescapably better for caves though.
I was planning to have a distinct background colour for each for each of the strata, getting darker the deeper it gets, but given the limitations of the palette recognise I may not have a choice.
The dirt looks a little noisy like it's unfinished, but you've got a more processed tile to the side. Is it in the process of being updated to match?
That's an earlier version. The more I work on something the noisier it gets.

Quick edit from Helm's with 3 versions. I don't say any of these is good, in fact I don't know how to solve the issue with this hellish palette.
The red and grey does look promising. Love the combination of the blue and brown, I'll have to find somewhere to use it.
EDIT:
Added a couple more variations.