is the background color bright white or more of an ivory?

It's more ivory, definitely. Not a bright cushion. I really like it -- but I'm not going for the bright, cheery look. It blends with stuff around it.

is there a slip cover in thus pattern

If by "slip cover" you are referring to the plastic liner shower curtain, then no, it's just the cloth curtain. I have a separate plastic curtain. Let me know if I'm understanding your question correctly?

Is the background white, ivory, or more of a cream?

This item is not ivory. I would say it is white but not a bright white. I repainted my bathroom black and white and the white paint is a true bright white so you can see a subtle difference between it and the shower curtain. This is a quality item and well worth the money. Hope that helps!

Are these panels lined?

These panels are not lined. I am getting roman shades with black out lining to go behind them, these are in our bedroom. I am still very happy with them. :)