C
Ceramico tiling
I would try wetting it thoroughly with white vinegar, neat - leaving it to soak in a bit and the dabbing it with white kitchen roll. If the black comes off onto the kitchen roll you are on a winner, so just keep on repeating - remember vinegar is used as grout haze remover, and you may just be lucky enough that the dies are locked in with the cement particles.
If this does not work, dilute the vinegar in the carpet with water and keep dabbing and soaking up, don't rub, as the fibres will become all felty, and won't recover later. I would then use plain household soap, wetted and dubbed on, again leaving it to soak and do the kitchen roll check. DON'T try the household soap before the vinegar, as soap residue would neutralise the vinegar, but you're ok the other way round. By now there should be some progress. I f not the other options are ammonia based window cleaner - (ammonia can have a bleaching effect, so take care!), nail varnish remover or cellulose thinners. Good luck, let us know the outcome! My bet is on the vinegar finished off with the soap ...
Thanks,, I just coppied and saved that for future use.