Hi, did you sort the white patches? Ive had the same happen to me. Indian Stone patio layed and looked beautiful. Then the cement pointing was done with a dry mix brushed all over, then brick acid to remove any stains, then sealed. Hey presto lots of white patches all ove rthe stone and a grey-ish haze which has dulled all the colours which were fine before. Not sure whether its the stone soaking up the concrete below, the sry mix brushed on, the brick acid or the seal so.... im getting the stone sandblasted back to an original layer which has not been treated and leaving it to let any natural chemical reaction to the underneath cement happen and hopefully in time they will look good as new. Thats the idea anyway which seems better than ripping it all up!