We do colour image processing in an RGB-derived spherical space with colour attributes given by hue, colourfulness
(as opposed to grayness and somewhat different from saturation) and lightness; we call it Runge space.
This spherical space is as intuitive as more common spaces of the type hue-saturation-luminance (called here
η,Ε,Λ spaces), yet it avoids the continuity problems of the transformation (R, G,B) → (η,Ε,Λ) that result
from normalizing the saturation by the luminance, or of having a geometrically nonhomogeneous space, when
the saturation is left un-normalized. We give Matlab routines for the conversions between colour spaces RGB
and Runge, and present applications of colour modification in Runge space.