Depending on how frequent you want to clean and maintain the area would affect how light or dark you want your grout. A lighter grout would eventually stain or show mold. A dark grout would be bold and define the lines of the tiles, but this look may appear outdated a few years down the line. If you aren't particular about being trendy, the dark grout is more practical.

I think dark grout is going to create a bold pattern that will be much too busy with your speckled granite countertop. I don't see why grout in this area would get moldy or stained. It is a rather small and off to the side area of your kitchen.

I think matching the counter is a good idea as the two chosen parts are a little conflicted style-wise…but you could choose a lighter shade from the countertop..perhaps the golden beige that is dominant in the counter…