We tiled our basement floor with a porcelain tile laid over a heating system. On the advice of the guy at the tile store, we said that we could just butt the tiles up against each other and not use spacers. That seemed like a great idea at the time. However, we can still see the lines between the tiles from the thin set. The thin set dried to a light gray color and our tile is a dark brown.

Can I still grout the tile to remedy this problem? Is there another solution?

Thanks in advance.