I had the same problems as you so I dyed the grout dark grey in my kitchen and dinning room and while it does look 100% better than it did I would not recommend you do this yourself.

• You're basically painting your grout. I don't remember how long it took but it takes much much much longer than what you're probably thinking and after you start it is too late to turn back so you have to finish. You also need to keep some of the dye on hand since if someone scrapes the grout by sliding a chair or similar action and it goes through the layer of dye, you have to retouch that section to make it dark again.

If I could go back in time I wouldn't have done it and would have instead got some quotes from a professional on how much it'd cost to re-grout the tile with a darker grout and also got some quotes on how much it'd cost to just rip out the old tiles and grout and put in new tile with a darker grout and made my decision based on those quotes.