> Quote - Explanation: If you stand in a church. In front of a colored window. You look down to the ground. You can see the light on the ground, falling through the colored window. It's colored in the same way like the windows !

Yup, we understood that.
Above is the same setup in Poser as you had in Carrara. You must have had shadows disabled in your test render.

Quote - Can you apply a coloured "gel" to a poser light ? if you can, then you could put a pointlight or somesuch in front of the window with the gel on it and maybe fake it that way

Yes, you can. That might work, with careful light placement.

"If I were a shadow, I know I wouldn't like to be half of what I should be."
Mr Otsuka, the old black tomcat in Kafka on the Shore (Haruki Murakami)