For the benefit of those googling for info on how much cementone / Travis Perkins mortar colourant to use...today when grouting up 100sqm of natural Indian stone setts/cobbles i used 1 kg, ie one tin per belle cement mixer load full of sand and cement. we used half a 25kg bag of cement per load measured in a bucket with and additional 4 of the same level of red sand per load. the instructions say we could of added another 1/4 of a tin, but that's as black as we could go.
Its about £6 a kg tin, we used 13 tins for a 100sqm area. That's grouting for around 8500 setts/cobles.
hope that helps!
steve