weird carrot cyanotype

I somehow accidentally did this when making postcards for the postcard exchange. Here's the details I've noted down:

BFK Rives Blanc paper, no pretreatment before coating with traditional cyanotype formula. Cyanotype was overexposed.
Washed cyanotype in weak (small sprinkling in a sink full of warm water) tartaric acid solution by soaking it face down for about 10-15minutes.
Hung it up to dry for a bit, decided it was still too overexposed and maybe if I use normal tap water it'll bleach back quickly.
Put it back in a sink full of warm normal tap water and left it another 10-20 minutes.
Come back to orange carrots on a blue background (wha..??) and think you've gone mad and printed too many postcards.
It's definitely not yellow that hasn't washed out (that'd be green not orange) so I don't know what the hey happened. Maybe something reacted with the iron-based cyanotype solution to create a sort of rust(oxide)?