I'm using Italgraniti material d forma Grigio tiles in my kitchen. MarmI imperial elegance Striato on the walls and stone mix Striato White on the floors of my bathroom. Any advice on grout colours would be much appreciated.

Okay, appreciate the advice given so far. Went to the local tile shop with medium grey and sand grout samples and found that sand was a different shade to the sample in the shop. After taking newer samples out it looks to be my tiler samples had discoloured. So in the end sand was much browner than I wanted. Below is medium grey and also a lighter version (manhattan). Also size of the job. Now wondering if I should go lighter?

I think it all depends on the look that you are going for - with these tiles, I too would be tempted to colour match as closely as you could, however it also depends on the style and wider context of the house. I have a Victorian house and old battered boards in our living room - they have gaps between the boards which effectively almost look black. When we did wood effect tiles in our en-suite, I bought similar coloured tiles and then used a dark anthracite grout to get the same effect as the living room. However the tiles you have chosen are a different style - they’re a lovely fresh contemporary wood effect compared to my old battered boards, so a more neutral colour that blends in would look fab!

Choose the one closest to the tile colour. No 1 or 2 I can't really tell from pics. 3 is a non starter unless you are deliberately looking for a grid effect. I think your tiles are grey rectified porcelain? If this is the case you can go as small as 2mm with your grout. This will make cleaning much easier. I had them once and they were fantastic. So easy to keep clean and very crisp looking.