Also the exterior is coyote brown so I don't think it would matter much.
Either way it's going to be a fair amount of fabric so I want to use the lightest thing I can find that will work. But not Tyvek. Something perfectly quiet and soft.
In the right conditions a sudden breeze can get you "rained on."
It's not a big issue to me as the 8 man is so voluminous you can stay away from brushing up against the walls pretty easily.
The liner acts as a vapor barrier. It might make it a little warmer, but very little.
So it's a purely a luxury item.