Princeton Architectural Press Cat Box: 100 Postcards by 10 Artists

Do these come with envelopes? I would use them as cards but would want to have envelopes as well.

Are these for coloring yourself? Or do they come already colored? I can't tell

What is the size of the postcards? Are they actually 4x6 or smaller? (Box size is not helpful)

Can you tell me the the thickness of each card? Wanting to get a number so I can see how stiff they would be sending them in the mail as postcards.