Complementary shading

The practice, Byzantine in origin, of rendering shading in the modelling of a figure or drapery in a complementary (that is, contrasting) color, rather than with a darker shade of the same color or with black. The technique often produces an image of greater naturalistic as well as decorative effect.

Michelle Brown

Michelle Brown. Understanding Illuminated Manuscripts (Malibu, CA: J. Paul Getty Museum in association with the British Library, c1994).