My kitchen floor tiles have been down for a few months now. The grout is light grey and it looked fine at first with the colour even throughout. However, the grout is now becoming stained in some areas, especially close to the stove where spilt fat etc has discoloured the grout. When I bought the grout I asked the shop if it needed sealing and they said that this grout did not need it. Is there anything I can do to improve the appearance of this and prevent further staining?