Hi Denise,I read recently that International Paints make a Grout Pen.I think you can get them at B and Q.They also do tile paint.Not sure how good they are though.
mix bicarb of soda & water into a paste- leave it on for a minute & rub off with tooth brush- makes it perfect white again (& is really cheap).
bit of elbow greace works every time (not sure where to buy it from though!)