I'm a huge fan of Standard's 551 porcelain. It's really white, throws well, and doesn't seem to be particularly prone to warping. It's happy to be thrown thin, tall, collars in well, and doesn't collapse easily like when you're making large wide bowls. I've colored it with mason stains which also worked. It's a bit more expensive than highwater's little loafers which I've also used and liked. The two of them are almost identical in terms of whiteness at all stages. I prefer 551 for throwing (by just a tiny bit), but the cost difference may not be worth it for you. Hope this helped some.