R

Recipe
A term used mainly in the dyeing industry to represent the combined colorants required to match a colour. In the paint industry other terms such as 'formula' are often used.

Radiance

Reflectance factor

Reflection

Reflectivity

Refractive index

Retroreflection

Retroreflector

RGB

Riemannian colour space

RLAB

Rods

RUCS diagram
Rectangular Uniform Chromaticity Scale diagram.