Quills Again

I'm off to get yellow on Porcupine Quills again. Hopefully this time it'll work. To date I've been able to get reds and blues, but no yellows. I want yellow, orange, purple and green. I'm using only natural dyes, no acid dyes. If this doesn't work I may resort to using acid dyes, I don't know though I rate hate to resort that, it feels a lot like cheating.