Grout sealer is not that important, It is better get the color coded grout match the tile's color, white tile is easy you can buy white grout, if your tile has different color and unable to buy same color grout. Here is the little trick, buy a small can (1/4 litter) of latex paint, tint it same color as the tile, mix the grout with the latex paint and some water, but not a lot, after all finished, the gap between tiles have matched color with the tile. I done it in my basement it works well.