Not sure if you know this J, but earth pigments in a hide glue binder is simply watercolor paint. Any traditional paint will work well: watercolor, milk paint, artist oil paint, and the various natural dyes and stains.
There are MANY modern finishes available that are waterproof, flexible, UV resistant, and durable.
Personally, I usually use shellac as a pigment binder and finish. I also use watercolors, tung oil, and beeswax.