Subbing roasted red peppers for beets would be a snap.
Vol 4 - p 287 Modernist Cuisine
If you don't have access I can paraphrase the gist of it but it'll take a bit of typing.
Cool - the prep / technique is on Page 295
it will give you the guide to using almost any kind of juice for a meringue.
It's Albumin powder - powdered egg substitute would make a hell of a mess...
no worries it's a subtle difference in naming - but it would make a big difference in the method!