Hi all,
You want 100% sphagnum peat ("Vapo" or "Bord na Mona" are good brands). I usually put the peat in a cotton pillow-case, and then soak it in a water butt, this way you can get the colour of water that you are aiming for by cutting the peaty water with RO or rain water. You won't soften hard water very effectively with peat but it does have some effect.
Another option are Alder "cones", they work really well and they are a bit less messy than peat. You can also PYO, and they are a more environmentally sustainable resource than peat. Tim from "TA aquaculture" has some Alder cone details on their web site.
cheers Darrel