Our design team suggest you keep it simple with Grout 11 Anthracite To highlight the black tones of the tile.
Alternatively we suggest you use Grout 05 Shadow to blend with the pale background.
Recommended Grout Joints - (We have assumed that your substrate has a perfectly flat and plumb surface, please check with your tiler.)
4mm grout joint. Based on this joint size, 1 bag of grout would cover 4.5m².