Is there a color standard for painted toroidal magnetic cores?
Colours are not an industry standard for ferrites as these recipes are proprietary and there are many variations of different materials.

You might want to contact the supplier for specs and if none, continue with your trial and error methods.  The most important aspect is often the power losses at certain temperature ranges in order to be thermally stable.

This major MAGNETICS company (by same name) simplifies their specs down to 4 different materials P,F,R,K

http://c1233384.r84.cf3.rackcdn.com/UK_MAG_ferrite_material_selection_guide_AN.pdf


I do have several books of hundreds of different ferrite samples from TDK, if anyone is interested in paying for shipping  them.