Tangerine Nightmare is no more. I dyed it. It was an interesting experience. Following Tammy's excellent advice, I dyed a swatch first. I am embarrassed to admit that this did not occur to me independently. Apparently, I am incapable of transferring even hard-won knowledge from one context to another.
Here is the swatch, floating in a bath of warm water, which I gradually heated to bring it up to dyeing temperature, in the hopes that I could prevent felting.
After it had warmed up sufficiently, I put it in the dye bath for half an hour, keeping the bath at a steady 140 F (60C). This was the result:
I know this looks black on the screen. In fact, it is a chocolate brown with purple undertones. It is interesting, but not quite what I wanted. So I prepared the dye bath for the sweater with twice as much dye, and took the plunge.
I simmered the sweater for an hour, stirring it gently and frequently and praying constantly to the Knitting Goddess to keep it from felting. And it didn't felt! Oddly, it also didn't turn black. Just like the swatch, it came out dark brown with purply blotches underneath where the original magenta was. I know it looks black in the picture--my camera does not recognize the actual color. I can't blame it; I'm not sure I recognize it either.
This is The Sweater Formerly Known as Tangerine, drying in the laundry room. When it's dry, I'll take a good look at it in natural lighting (it's still raining and once again 4:30 pm here). There is a decent chance that it will end up being a pretty heathered espresso sort of color. But in the event it ends up looking more like dog poop, does anyone know whether I might have better results with a different dye? I used RIT dye from the grocery store (don't laugh), which I understand is a combination of two types of dye, only one of which actually works on animal fiber. The preferred dye for animal fiber is acid dye, which I didn't have. Can anyone tell me whether it would be worth trying to overdye it with acid dye? Advice is quite welcome. In fact, I probably should have asked for it, um, earlier.