Tiling/Grouting advice needed

Are there any professionals out there who can give me some advice on grouting please.
We've tiled and grouted the new bedroom and it was husband's bright idea to use a coloured grout - in this case, terracotta. The problem now being the terracotta has faded to a dull pale reddy colour. Is there any product which I can use to darken the grout and keep it dark. I've tried to varnish it and at first it worked okay but after a few days it reverted back to the grotty pink.
Any advice would be appreciated. Thanks.

Im not sure hun, white goes the same way, only thing I found is to take off the surface and regrout...which is time consumming.

Do the DIY' shops have anything, might be worth giving them a call.

You can apparently buy grout dyes/stains (unless that's what you mean by varnish?)

No we just used colourless varnish. Might have a look online then thanks.