You probably want to make the sky a backdrop, which is something that can be in more than one place (see ยง3.9 in Writing with Inform). That way you only have one description to modify when the sky changes appearance.
If you want the sky to be visible in every room, you can say
The sky is a backdrop. The sky is everywhere.
If you don't want it visible in every room, you can just put it in certain rooms or regions:
Outdoors is a region. The sky is a backdrop. The sky is in Outdoors. The sky is in the Sunroom.