I would recommend a grout i have used in my bathroom and are currently using in my kitchen. It is called 'Mapei Ultra Color Plus'. It Flexible, mould resistant and water repellent. TBH i can't speak highly enough of it.
I think the last .lot i got was �7-8 for a 2 Kg bag which was enough for 6 square meters.
I don't know where you live but i got mine from a place called Tubs and Tiles in Coventry.
Hope this helps.
Oh yeah, it comes in about 25-30 different colours as well.