coloring existing grout

[99-1093880100]

Hello,
I stumbled on to this site, which is really beautiful and complex! Great site.
I have a problem: my fieldstone home is 80 years old - in America, that's pretty old. The original grout is a light beach sand color. I had some stonework done 15 years ago, and the mason matched the mortar perfectly using white cement and calcium based sand. I recently had some repointing done while I was away, and the mortar came out very light - almost white. I want to darken the the color to match the original. I even brushed on some strong coffee, and the color was perfect! But, of course, it didn't last.
My question: is there a way to make a liquid that I can brush on the joints to darken the color so it matches - and lasts?
Any help is appreciated.

Chuck

[84-1093879891]

Not as far as I know - certainly not with British or Irish products. There may be something in the States, but, as I'm not familiar with the market over there, I really can't say.

[99-1093880100]

Thanks for trying. If/when I can find something that works, I post it!

Chuck