This was some bare Falkland that I had spun into a two-ply. I soaked the skein in citric acid while watching a few online tutorials. These were the most helpful for the kind of result I was hoping for:
Camaj Fiber Arts
I used Greener Shades dyes, which are heavy-metal free. I mixed the dye in squirt bottles and applied the color using those. I think the trickiest part was rolling the yarn up into the plastic wrap, but I made it work. It went into the steamer pot for about 35-40 minutes, and then the dye was set!