Full Idea
I am assuming that even in those contexts in which the presupposition of 'the number two is green' fails and the utterance is infelicitious, it nevertheless receives a bivalent truth-value (presumably 'false').
Gist of Idea
Category mistakes because of presuppositions still have a truth value (usually 'false')
Source
Ofra Magidor (Category Mistakes [2013], 5.4.1)
Book Reference
Magidor,Ofra: 'Category Mistakes' [OUP 2013], p.132
A Reaction
It seems to me obvious that, in normal contexts, 'the number two is green' is false, rather than meaningless. Is 'the number eight is an odd number' meaningless?