As it says really:
Color is pure white… Any ideas?
seems so. but you can try it in a composting-node-setting and see how it looks then. (you have the denoiser aktive? in the past the denoiser didn’t worked well with shadowcatcher, but it should be fixed…)
Would you care to share a file? :eyebrowlift:
Works here. Tested with 2.79 RC2.
e.g.
Indeed. File a bug-report!
edit:
for some reason it looks less evident with spheres, but it’s still there: you can see on a white background shadow pixels calculated that eventually get cleared and look white
yes, shadows catcher behaves a bit strange - but it’s better to use something than nothing
in your case either
- strengthen the point light
- widen the gap, enlarge the distance between planes
ps
seeking problems is not hard, you will always have at least one, human 
it’s about having a solution when you know what you want, have an intent :yes:
Seems to now be working as expected in 2.79 