Noble Color

A name for inborn special talents, used within the Association.
Primarily used in reference to those who possess mystic eyes. For instance, the mystic eyes of Tsukihime's Shiki are an example of a Noble Color.
Rider's mystic eyes of petrification fall under the classification of “Jewel,” which exceeds even the “Gold” possessed by the highest class of bloodsucker.
Further, beyond Jewel lies “Rainbow.” These ultimate mystic eyes, which blend and mix all seven colors of the rainbow like a kaleidoscope, are considered to be the mark of the King of the Moon.

Fate/side material: Fate Encyclopedia