The secret to less maintenance with grouted tiles of any color is using grout properly mixed in order for it to not be porous. A grout mixed soupy will be porous versus a grout mixed to a thick consistency. As the grout dries air bubbles come up through the grout leaving pin holes to trap dirt and hard to get clean. It is very difficult to properly seal a porous grout.

You are correct that you cannot use bleach or most cleansers with marble tile. You should look into the porcelain tile made to look like marble. It has come a long way.

Cementitious grout will always be porous. Grout sealer does not keep grout from getting dirty. It merely buys a little bit of time to wipe up a spill before it stains.