There are several ways you can do this. A lot of fellows on here use Rite dye to accomplish this effect. I use a soloution that I make from dried onion skins and apple cider vinegar, and as has already been said you can use tea bags.
just go slow so you don't get it too dark.........you can always add more colour, but it's difficult to lighten it up if you go too far.
Soggy
OPPPS!........looks like this post should be in the "Craftsman" thread........you're asking about "makin" not "using" a horn