I also have the same in my kitchen,l like all the suggestions listed!

I find that bicarbonate soda and vinegar is good as a natural alternative. Jiff will get them clean but not as natural.

I use the Jif cream cleanser (same one my Mum used to use many years ago!) I also find it great in the shower.

Gumption is great but if you are looking for a more natural method give lemon juice, vinegar and bicarbonate a go.

there are some pretty good answers in here, so I won’t go over what they have said, just try them if one works fine, although a little steam cleaner may work, may be easier to scrap it out & re grout

my husband got a grout scraper and took off the top layer then refilled with new grout. sounds time consuming but it only took him half a day to do all our bathroom and it looks like new!

The grout may not have been the colour you think it should be. If the tiles are the same in another part of the house check the colour there. White Vinegar is very good. It will kill any mould if there is any/

I bought a grout pen (made by White Knight paints) & it brightened my kitchen grout.

Vinegar is usually pretty good. It also kills mould far better than bleach does and is cheap. Good luck. I hope you don’t need to re-grout.

An old toothbrush dipped in white vinegar does a reasonably good job of cleaning up the grout and the smell evaporates after drying.

Try some bi-carb soda mixed with vinegar to form a paste apply with a toothbrush

sometimes it can be the grout itself. the only solution is to re-grout. my friend just had to do this to her bathroom as she had tried bleach, gumption, sugar soap, jif, white king- you name it! a plumber friend of hers recommended re-grouting it. not a tough job it turns out. if you are renting and concerned, just let them know that you have tried everything.

I would suggest taking a photo and taking into a tile store; they will be able to advise you; it may depend on the age of the tiles and grout?

Try a steam cleaner

I would try two products at separate times not together. First try would be Sugar of Soap and if that doesn’t work try undiluted dishwasher liquid. I would use steel wool to work it into the grout. Good luck.