May I offer the following works as guides/information sources as to the use of white in frescoes:-
"Materials & Methods of Painting" by Lynton Lamb
"The Materials & Techniques of Painting" by Jonathan Stephenson
"Plastering, Palin & Decorative: A Practical Treatise on the Art & Craft" by William Millar (pub 1897)
"The Art of Fresco Painting" by Mrs Merrifield (pub 1846)
"Fresco Painting - Its Art & Technique" by james Ward )pub 1909.
In olden days the plasterers used to have a lot to do with mixing up the colours too so although some of the books I have listed would appear to be strictly plastering books there is some very useful information for artists too.
Let me know how you get on.