Your hair is sentient and has taken on a life of its own.
Well, it's always had a mind of it's own!
I have no idea either! Definitely very strange.
Aliens perhaps, or bitten by a radioactive spider?!
I had the same problem as Janineb, my base was pale blonde and was stripped to dirty blonde in some places (others have just gone muddy green but that's normal)
I used a color B4 on top of that and the darkened bits turned back to their original colour.
I forgot to take before and after photos and I know this thread is really old but I've just done this method to get rid of some Crazy Colour Blue Jade and it's removed most of it and left me with a pale green tinge which I'm going to cover with a box dye in my natural colour because my hair really really needs a break.
But thank you so much for posting this method!
Oh, I wish I'd knew before the powder + hot water technique!