I would colour match the grout . Looks better I think imhoI don't mind cutting the plinth as I have the right gear to cut off what I need.
So a 3mm Silicon join to the skirt will be ok then. I have found a good Silicon match to the grey tile colour and will be using a darker grout.
My thinking was that as it looks the same colour its almost likeI would colour match the grout . Looks better I think imho