My patio use to be a lovely light yellow but now've lost their colour, but when wet they all go a darker yellow which looks nice. I was told to use a water seal which I got cuprinol water seal, it looked great when I applied it, but now they've dried out, they have a bit of colour with grey patches and some have gone completely grey, they are dull and dirty looking even though I gave the patio a jet clean a few times and waited for it to dry out before I started is there anything I can do to get a even colour they go when wet or at least get rid of the grey patches. Thanks