Sorry Goldzilla, didn't see your question tucked under that huge pic
I think the trim colour code relates to the door and roof trim as Terminal has stated, and also the dash and carpet colour.
There's two codes, Z and J. I know from mine that Z is black dash, console, door skins, grey roof and rear trim, dark grey carpet.
I think J is lighter colours, someone who has this trim would be able to describe it.
The only other differences would be the seats and the fill on the doors, which is dependant on model or options (eg, leather).