For me, I used a mixture of glue, water, baking soda and white paint to make snow with some snow effects fluff sprinkled on top of the mixture after applying it to a surface.
If you're considering the same thing, I've not had my baking soda yellow yet... but my glue sure did on a few projects. Be sure to test out a few different types of glue to avoid the yellowing. I find Aileen's Tacky Glue doesn't yellow and works great for all kinds of stuff anyway.