Floor grout staining issues.....

OK, I've tried the search and not got a result, so I thought I'd ask....
I have about 65 sqm of floor tiles with a light grey grout (what was I thinking???????!!!!!!) which I stupidly chose not to seal after putting it all down. So, 12 months later in a house with 3 cats and a dog, all with their fair share of puking, plus red wine spills etc etc the light grey is every shade up to black in places.
I know I can spend days on my knees trying to clean it up with bleach or some such other product and a brush, or call someone in to do it for me, but what I really want to know is, seeing as it's porous, can the grout be stained now it's been laid for over a year? Is there a product I can brush on that will soak in and stain it permananetly. Ideally I'd like it a very dark grey colour, which I'd then seal. I've tried Google, but only found info on companies who do stuff with cleaning grouting, and dyes to colour grout before it's put in.
Thanks in advance.......