A threat/ power level designation system used by S.H.I.E.L.D to categorise extra normal entities.
Based of the colour spectrum, I ROY G BIV V UV, with the colour rating the power level and a following number between one and ten rating the threat level (1 = safe, 10 = extreme and hostile)
Infra Red
Red
Orange
Yellow
Green
Blue
Indigo
Violet
Cull, for example would be a UV10 designation, while a human normal child would be an IR1.