I never got the hang of layering watercolor. :b I'd think lifting with tissue or similar'd be less risky for lightening, but folks other than me seem to do fine using gouache. ¯\_(ツ)_/¯

In my experience you need the good stuff to do more layering. 100% watercolour paper. I don't tend to lift a lot, you tend to get a smudgy edge and run the risk of lifting more than you wanted to. And it depends on the paper. Its probably good if you want to lighten a larger area though.
I think gouache might have the same weird blue effect since its similar to poster colour, but its worth a try. Might use acrylic if that doesn't work

100% cotton?

The big thing I hated about Cotman was that it's so hard to get the pans to dissolve--though I realized later that it'd probably make them a bit easier to layer. Never invested in them further to find out though. My experience is oddly broad and shallow; I've played with a fair bit of things (and read stuff), and every so often that's been useful for ideas, but with very few of them do I have any depth of experience..so sometimes my suggestions wind up being uselessly pointing out the obvious or just off-base. :b I can't help wondering though, what color(s) did you use? (I'm assuming any/all were in the Schmincke granulating range in any case, whatever the color(s), since you seem to favor it.)

Woops yeah i meant 100% cotton
I had the same frustration with cotman pans, i think they just suck.
I used schmincke's neutral grey and graphite grey. I didn't use their granulating range for this one but I do like them!

Aha! Neutral grey uses benzimidazolone orange, coral red, and indanthrene blue, the latter being an organic staining dye and could be seeping preferentially into the white. The sort of greyscale noodling I've done has mostly been with sumi ink or that Tom Norton faux-walnut ink, using different dilutions; since sumi ink's pigment is essentially soot, you might be able to accomplish the same with dilutions of ivory black if you have some of that already. Or the graphite grey by itself, though graphite's kind of an oddly behaving pigment sometimes IME, outside of non-soluble pencils anyway.

I think I do have an ivory black that came in the original set I got so I'll have to try that instead, thanks!
That's a pain though, I do like the look of neutral grey

Probably no reason not to use the grey if you don't use white with it! Maybe sucking excess up into a clean damp brush would help lighten areas with too much pigment--though you'd have to catch it while it's still wet.

Yeah I do that for larger mistakes, what I use the white for is little detailed highlights. But yeah I'm still experimenting with grayscale paintings, I'll just have to accept I'll need to be careful if I'm using that paint.

👍 As always, look forward to what you come up with next, even if I'm suspiciously quiet when you do.

Oh! And maybe misket/frisket or wax for blocking highlights ahead of time? Not so good for planning mistakes ahead of time though..