have you given the grout a chance to dry completely?

Are they diff tiles? Was the grout line specified to match? Olive would be a drab colour

The tile grout looks olive to me. Which you said you chose.

why did you choose a different colour to existing tile grout?

The existing grout colour is also Olive. So the grout should look the same. In some places it looks almost the same but most of it looks like the photo.

The tiles were laid a couple of months ago. So grout is dry. The tiles are the same and the grout colour is a great match as you can see in the comparison photo. I tried to clean the grout and the cloth comes away dirty and the grout crumbles and comes out from in between the tiles.

Hi Tracey, in your original post, you said you had "just" had your tiles laid, that is why I suggested letting the grout dry.

but now your saying that it was a "couple of months ago"

so, if that is the case I would return to the tile shop, explain your grout issue, and ask if they can refer you to an expert that could analyse what the issue is with the grout.

since it's been a couple of months and the grout should be the same as the other older grout, then there is definitely an issue, which you need to address with a professional.