FAQ: "I need to assign an EP Color rating to a powder we have in the lab. Can you advise on this?"
The EP Color scale is typically applied to clear transparent liquid samples, not to powders in reflectance. It's not that you can't measure the color of powders using color scales like CIE L*, a*, b* D65/10 or Whiteness Index WI E313 D65/10, but not with the EP Color Scale.
One option to measure in EP Color is to dissolve a fixed amount of the powder in a clear transparent solvent; standardize the instrument in TTRAN Total Transmission on the cell + solvent, and measure the EP Color of the clear sample solution.
For more information on EP European Pharmacopoeia Color