2nd Gen Cavy convertible-Moldy carpet problem

So I hadda clean the mouse nest outta the right side cowl drain to open it up again.
Trouble is now I gotta kill the crap living under the floormat... Anybody ever had this problem know of a good way to kill it without doing too much damage to the color of the carpet? I suppose I'd hafta bleach the gunk to kill it and then re-color that area under the mats...

Has anybody tried that spray carpet dye? The bleach is gonna take out the color, I know-so I figured I could try this stuff. I really don't wanna disassemble the interior just to redo an area under the mats.

Any other ideas/hints for dealing with the black gunk that lives under the floormats would be greatly appreciated.