know of any good
>limeproof pigments?

Try kremer-pigmente.com. They have a list of known stable with lime pigments. There are others I have discovered - some pretty exotic - like ground up holographic film, and a beautiful, glow in the dark, swimming pool blue.

White pozzolan sound interesting. Lots of Flyash here - cheap, industrial byproduct, less than portland cement. A light brown color.