I happened across a reference to the Saltpeter War earlier today, and after attempting to do some follow up I haven't found much information beyond some brief, confusing references to Tangaxuan II (was he the cazonci at the time or not?) wanting to control sources of saltpeter in Colima and Jalisco. Why would the Tarascans start a war over access to the saltpeter? What were they and other Mesoamericans using it for?
This is the first I've heard of this. Or rather, this is the first time I heard it called this. Tangaxoan II was only on the throne for a brief window of time between 1522 (when the last monarch Zuangua died of smallpox) and 1530 (when he was deposed by Nuño de Guzman and the monarchy abolished). During this period, the Spanish basically left the Tarascans alone while they focused their efforts on subduing the Pacific Coast. The peoples in Colima proved rather troublesome, and the Spanish enlisted Tarascan aid in subduing them (a task which wouldn't be finished until after Tangaxoan II had been deposed). The Tarascans had previously attempted to conquer Colima, but after the disastrous 1476 war with the Aztecs, they decided to abandon their plans for expansion to the west and north and refocus their efforts on defending their eastern border.
So the Tarascans involvement in Colima during this time was largely restricted to providing support for the Spanish. Also, the Spanish had to pass through Tarascan territory to get there. If the conflicts had anything to do with saltpeter, it was likely the Spanish who needed the resource. Beyond that, I really don't have any more information. Colima is a bit outside my main area of focus. /u/Mictlantecuhtli works in that region (albeit in a much earlier time period). He may know more.
So I've combed through the primary sources. There are only two mentions of Tarascan involvement in Colima. The first is in the early 1470s under the reign of Tzitzispandaquare, and the second was in assistance of the Spanish conquistadors under Tangaxoan II, in the 1520s. There is literally no other mention of Tarascan involvement in Colima in the most comprehensive primary source on the Tarascans, nor in any of the secondary sources I have. And certainly no mention of saltpeter. I have no idea where this idea comes from, but I'm really curious now. It's possible this Spanish-langauge encyclopedia they're citing in the wiki is drawing from a primary source I haven't heard of, but I'm really skeptical. I have a rather comprehensive collection, and the fact that it's not mentioned anywhere makes it rather suspect.