what are you starting with? easiest way to make white paper is to start with white stuff.
it's going to be hard to get it white if you're starting with something that has ink on it, like recycling copy paper or newsprint.. the most practical thing to do if you want to wind up with something that's a pretty color is to toss in something.. colorful.. like a colored napkin, or a colored flyer or a sheet (or part of a sheet) of colored tissue paper. try adding something colorful, a little at a time, until you get something that looks pleasing.
what are you making? sheets of paper (dipped, or poured?), or are you going to do a casting? what's the finished project going to be?
fun stuff, making paper.