Limestone colour enhancer - Black residue on surface of slab

[Segster]

Hi - We had a limestone patio laid last year and in order to keep the colour as dark as possible, the contractor used some brand of colour sealer/enhancer about 8 weeks after it had been installed. The enhancer did the trick as the stone went considerably darker - however whenever we went out and walked on it - we all ended up with very black feet! On inspection, there is a residue of black powder left on the surface which is proving very difficult to get rid of. I've tried rubbing it off with a cloth and also tried water and a sponge mop (which turns the water very black!) - but no use.
The guy who did it just used a fence sprayer and saturated the whole patio - then left. He did say that it would just soak in a seal itself - but that doesn't seem the case.
Anyone come across this before and know how to fix it? thanks

[Tony McC]

You've been done.

Some con merchant has sprayed a water-soluble dye and taken your cash.

It will need professional cleaning and then treating with a *proper* sealant, preferably applied by a reputable tradesperson.