Let's say
Taxonomy_A is associated to Node_Type_A
Taxonomy_B is associated to Node_Type_B.AND
Both Taxonomy_A and Taxonomy_B have a term called 'yellow'.
Is it possible to make terms 'yellow' synonymous, so that if I'm looking at a list of 'yellow' stuff, I'm seeing content of both types (Node_Type_A, and Node_Type_B)?
Progress:
Unfortunately it is not possible for taxonomy terms to behave in Drupal as described in my question (at least not without forcing it):
It is clear by taking a look at the terms_related table that it would be possible to create paths that forced related terms together using the taxonomy_get_related
function regardless of what vocabulary the term belongs to:
However, the way to get to these terms is through the taxonomy_get_related
function in the taxonomy module. This function is not used at all in drupal-6 core except to define it. (I did find it once in the ctools module).
I think you are doing it wrong. I mean using taxonomy wrong, not technically, but as a concept. Ask yourself why do you have 2 vocabularies with term yellow? Both are colour. they belong to same dictionary. Maybe tell little more of what you are trying to make.
Maybe you need to change setup so you don't associate one dictionary to one content type, maybe CCK, views and this module can do what you need http://drupal.org/project/content_taxonomy