Move the drying mat? It’s possible if you stop using it the counter might even out eventually. I love the material you chose. I’m a huge fan of the terrazzo look.

With posts like yours (there are many) I’ve always wondered whether switching to a mat made of diatomaceous earth might help (and it might if the issue is trapped moisture beneath the mat) but even those use silicone feet, and it’s the silicone/plastic that is the other possible cause of the discoloration, leaching chemicals into the resin of the countertop.

Show your drying mat? How long has it been sitting there?

Nothing as far as I am aware to remove that mark.

Not to the stain... but consider getting a low cookie cooling rack to go under your drying mat. Give a little air space instead of setting the mat directly on the counter.

That’s a great idea! Thanks.

If it is mold from damp, bleach will remove. If that does not remove, it is a color from the mat. Make a paste from Bar Keeper's Friend and using a damp paper towel, gently rub.

If neither work, it maybe a permament color transfer. Try the cooling rack or a wood drying rack.

Also, contact the manufacturer.