Can you confirm porcelain or unglazed ceramic? Do these come as sheets or individual tiles or larger tiles. Perhaps the guys can determine this from the photo.
My concern with a colour enhancer if it were an unglazed tile and will also have minor porosity, is also these can send pale or white tiles slightly grubby looking.
If this was the case , why not just put a suitable simple impregnator for water and oil reppelance .this will generally not change the appearance.
