While most homeowners don't know the difference between cementitious and expoxy grout, it might supprise you that most contractors don't either.
The problem with most grout you've probably seen is that is stains over time. It can crack, mildew, mold, turn colors,and chip out completely. Most people just accept this as part of having a tiled shower or floor, but this isn't the case anymore.
There are better products on the market in 2016, and most of the industry isn't keeping up. We use grouts that combine the look of cementitious grout with the elesticity and stainblocking power of exopy grouts, Fusion Pro is one of our favorites.
Don't get me wrong, this grout is more expensive, and it is a pain to install on tile. However, you can use lighter grouts and rest assured that they won't turn brown in two months. Check out this short video about Fusion Pro.