This time, I left out the red and it matched much better!
On the left is the fiber with the target color, on the right are several thinner ropes of roving that I dyed with 1/2 tsp brown and 1/2 tsp yellow. I also dumped in leftover brown and yellow from November when I was handpainting some yarn. But they were relatively weak and had been made originally from only about 1/4 tsp of the color in each case, and I had only probably half of the original quantity remaining.
Oh boy! I just realized I forgot the vinegar altogether! I just never remembered to put it in! Damn! I better go do a short vinegar soak so maybe they will still be colorfast. They took up almost all of the dye, although there was some left in the pot and now I understand why.
Anyway, the color is much closer to what I was going for, and I'm pleased.