I've used the silver grey Mapei Ultracoulor Plus grouting over white tiles. I mixed the grouting measuring the powder and water precisely to ensure that I get the same consistency throughout. I mixed 2.5kg of powder at a time and grouted as I went along. The first section of the wall looks lighter than the rest of it. I initially suspected that the two bags of grouting were from different batches which might explain why I got this problem. But then I re-grouted a lighter section using leftover from bag used to grout the part of the wall that looks darker and hey presto, it looks lighter this time! Can anyone offer advice, let me know whether I am doing something wrong?