Found this thread while looking for an old thread I had created with the same thing happening to us (Pink lines on stucco - help needed - #5 by JimLuke) . and guess what? it happened again today 
Since we’re probably going to have to get it painted I went ahead and told my guys to throw the arsenal at it: OneRestore, every single product that F9 makes, graffiti remover, 12.5 undiluted bleach, you name it we tried it. Pink hue still there… the only thing I haven’t tried is a bleach neutralizer. From what I could find online is the bleach reacting with iron deposits/particles in the paint and making the actual bleach turn pink and dying the surface.
There is no way to test for this (that I know of). luck of the draw really. But is uncommon enough that is not a huge deal. I’ll come back and comment again if we happen to find a solution other than painting.
