The KNO3 solution is actually yellowish, it has always been like that. I got the powder from a local fertilizer shop, I think they use it as a fertilizer for growing fruit.Fluo,
I'm wandering what kind/producer of KNO3 are you using. So much time I have ordered that chemical compound but all the time, water solutions used to be transparent but not yellowish like yours. It's possible that I've made mistake regarding the ferts you have on the picture above.