I think you said your blocks are complete, or you are working on them, so replacing fabric doesn't seem to be an option. Question: how wrinkled is wrinkled? Remember it's cotton, and cotton does wrinkle.......the darker fabrics maybe not as much as the dye has stabilized, but the cream is near natural fiber color, so less bulk in the threads.....I personally would not starch, either lightly or cardboard stiff....just keep working on it, when the piecing is done and you are ready to sandwich for quilting, just press ad usual, and continue the process......when finished it will be lovely. Don't sweat the small things...it's not worth it.....