Purple Fringing is also associated with UV, overexposure and overspill into adjacent pixels on some sensors, so that's only partly true.
I found an old message I posted in a discussion a while ago, which illustrates spherochromatism:
"One of the test images was a slanted close-up of a black and white print at f/2.8. The centre of the image is dead sharp; the top of the image shows a green bloom; the bottom of the image shows a magenta bloom. It seems that the bloom is a by-product of the lens being out of focus (due to the shallow depth of field)."
So, the effect is green or magenta fringing, depending on whether the object is behind or in front of the subject of focus. Contrasting edges behind the subject will tend to have a green bloom.