Why does the blue paint look like this?

[Koen G]

I'm not sure if this one has been mentioned before, from f37v. See both flowers, but especially the one on the right. Did the thick blue paint flake off to reveal a greenish underlayer?

   

I guess this can still be explained in two ways, as the blue being an overpainting meant to completely replace the original color, or as an attempt to "layer" two different colors to get some kind of effect. But I find this particular example to be quite... revealing.