I used Nexus Projoint Mid Grey Porcelain grout on our patio and it hasn't come out quite as dark as I would like. I should have gone for the darker grey, the mid grey looked great initially but its almost exactly the same colour as the tiles now that it's cured. It looks great when it's wet though so I wondered if I could use something like Lithofin MN Colour Intensifier, just on the grout to darken it up, hoping that it would end up the the same kind of tone as when its wet. Is that likely to work?