I was putting the final finish on some cabinets and ran out of rack space, had one more over the stove cabinet to do. Not the sort that can sit and watch paint dry I went out to the garden and trimmed a few tomato plants. Came back in to the shop and the other cabinets were dry enough that I could move them and I made room for the last cabinet and sprayed it. Came back a while later and the white paint had yellow in spots, kind of blended in but stronger at the edges.
I scratched my head for about an hour trying to figure out how the yellow got in there, had not sprayed any yellow in years, and besides it was the same paint in the gun as the rest. I went in the house and was washing my hands and the suds turned yellow. AHA! It was from the tomato plants, something I obviously would not have thought of. I usually run my hands over the piece lightly just before I spray to see if I can feel any imperfections. Now I know.