I actually thought this might be easier to understand than inspecting the argument. My rationale was that `collection` has a zorder defined by the kwargs anyway, or a default if it wasn't given so just getting the zorder from `collection` covers both cases, but then it gets weird when you try to avoid passing the zorder argument to `pcolor()` twice!

I'm happy to change this, it might be easier to understand in the way you suggest. I think I understand your explanation; as long as you are happy that this is a sensible idea in general then I'm satisfied.