Inscription is going to be going through some changes in Cataclysm. We've already had a pretty massive overhaul in patch 4.0 with the changes to glyphs, but we're in for some more after the expansion ships. Obviously, the mats we use will change: the new common pigment from milling is Ashen Pigment (for BlackFallow Ink), and the uncommon one is Burning Embers (for Inferno Ink). Kaliope, who I've come to rely on for beta profession information, informs us that the best herb to get the Burning Embers from is Twilight Jasmine, found in the Twilight Highlands.
As in Wrath of the Lich King, we will be able to trade the common inks for the uncommon ones; Jessica Sellers has updated her price list to accept Blackfallow Ink. It's going to be a single Blackfallow for a single older ink, as well as 10 for an Inferno Ink or Snowfall Ink.