It sounds like newsprint paper is the way to go for you. It's blank, and often a nice cream color so it wouldn't look terrible.

For any homemade cage, a bedding dam of at least 2" is essential. It keeps bedding from being pushed out so you can use the loose substrates, like aspen, and still keep your sanity not having to vacuum every day.

Carpet is not the best choice as it can harbor bacteria unless you can totally disinfect each piece every time you clean it. Look into plain newsprint...I think you'll like it.