Colouring or Staining Floor Grouting?

[227 BHA]

I have floor tiles in my kitchen with grey grouting. Some of the grout is old and some is newer where it has been repaired. I repaired with a flexible grout in the kitchen where there are floorboards under but in the utility room which continues thru there is a solid floor under and the original grout is still perfect.
It is now all in excellent condition except that the new flexible grout is a much darker shade - what can be done to stain the original or re-stain the whole lot into one uniform colour?

 

[smiths]

There is a product that colours grout, but I find it looks painted. You can always scrape out the old grout and re-grout. That's time consuming, though unless you have the proper tools.