HG sealers and lithofin are the best,if you look on Ebay youll find loads of companys selling them,we sell the HG impregnator @ £15.99 in the shop so i guess any cheaper on there would be good.
Grey is the way,white will discolour,we sell Granfix Maxi-grout anti mould white grout,great on walls,not so good for floors. :) Also please check that your polished porcelain is pre-sealed,if not seal it!!! Youll be sorry if you dont.