Over-dye in Reverse - Indigo & Yellow Onion

In the usual way of things, if you want green from natural dyes and are using indigo, typically you dye with the plant material that will give yellow followed by over-dyeing with indigo. The reason being that indigo tends to be a very strong dye and it is easier to control color and depth of shade by using multiple dips of indigo until you have the green you want. In this case the yarn had been dyed with indigo by a fiber friend who told me it was crocking badly and wondered if I could try dyeing it with the leftover yellow onion dye bath from one of my on farm dye days. Thinking this would be a fun experiment, I readily agreed. My first step was to wash out the excess indigo using synthrapol - it took a lot of rinsing, but eventually the rinse water was much lighter. I then gave the skein a bath in 20/80 white vinegar/water which yielded a clean rinse. The next step was to heat up the leftover dye bath and also add back in the fine mesh bag containing the onion (removing the bag of wet plant material and allowing it to dry prevents mold). The yarn was simmered for 30 minutes and allowed to cool down in the dye pot overnight prior to final rinsing. The two pictures below show before and after - definite darkish green with blues. The small skein in the lower second picture is one that I simmered after the indigo skein had been removed; the purpose was to see if I could still get yellow out of the dye pot, which clearly was the case. The great thing about this kind of experiment is that the yarn goes back to the original owner and I don't have yet another dye experiment skein for which I don't have a purpose.