This part of ISO 105 provides a colorimetric method for calculating an estimate of the magnitude (and optionally the direction) of the change in the perceived colour of a textile specimen when the chromaticity of the illumination by which it is viewed is changed. It therefore provides an estimate of the colour inconstancy of the specimen. NOTE 1 Colour inconstancy and metamerism are related but distinct. With respect to a change in the quality of illumination, a) colour inconstancy is the extent