Full Idea
It is almost universally acknowledged that Wittgenstein's plan to show all necessity is logical necessity ended in failure - indeed foundered upon the very problem of explaining colour incompatibilities.
Gist of Idea
Wittgenstein's plan to show there is only logical necessity failed, because of colours
Source
Fraser MacBride (Truthmakers [2013], 2.1.4.1)
Book Reference
'Stanford Online Encyclopaedia of Philosophy', ed/tr. Stanford University [plato.stanford.edu], p.14
A Reaction
I'm not sure whether you can 'show' that colour incompatibility is some sort of necessity, though intuitively it seems so. I'm thinking that 'necessity' is a unitary concept, with a wide variety of sources generating it.
Related Idea
Idea 9442 The only necessity is logical necessity [Wittgenstein]