Our designers suggest you select either.colour 10 Dark grey to match the grey base colour. https://www.bakedtiles.co.uk/products/fugabella-color-grout-08-cement-3kg?_pos=3&_sid=fd5d61930&_ss=r&variant=31378500485254
Or colour 11 Anthracite if you wish to add drama.
Recommended Grout Joints - We have assumed that your substrate has a perfectly flat and plumb surface, please check with your tiler.
3mm grout joint. Based on this joint size, 1 bag of grout would cover 6.3m².