Have you tried setting the default appearance of your stereotype object?
Yes - I can do that and it works, but as i indicated this then overrides the inheritence. Specifically the base stereotype is yellow but my stereotype gets the normal class orangey default colour. If I set the default appearance of my stereotype to yellow then I do get the right yellow colour when use the stereotype. *But* if the base stereotype is changed in the future then my stereotype won't inherit that change.
When using shape script, did you call DrawParentShape rather than DrawNativeShape?
I'm not (explicitly) using a shapescript, the shapescript is inherited fropm the base stereotype ancestor. I am only extending the stereotype to add attributes / tagged values so I want the shapescript behaviour to come from the ancestor. This is working, the stereotype gets the shape appearance - just not the colour.
Specifically the base stereotype is Archimate2::Archimate_BusinessFunction and (from the MDG XML) this stereotype has the yellow bgcolor set. So somehow the new stereotype seems to inheriting all the shapescript behaviour from the base stereotype *except* the bgcolor.
** Note this is with v12, I am working through the process of getting us upgraded to v14 and there might be some changes to this behaviour (although that would imply that the behaviour I'm seeing is an EA bug with v12)