What is color inconstancy?
Color inconstancy is the change in color of a single sample under different lights. The magnitude of color inconstancy can be defined by ∆E CMC of the sample between two lights.
The ISO standard for shade (in)constancy is called CMCCON and it refers to the ∆E CMC for a sample between D65 and a second light source. Given the CIE L*a*b* values for a sample in D65 and in a second light source it is possible to calculate the CMCCON for a shade.
As shown on the right, product color can change significantly in going from store light to daylight. This change can be unexpected and could leave the consumer less than satisfied with their purchasing decision. Therefore, color inconstancy is a problem that needs a more complete analysis.
Archroma Match Pantone® Colors – A SMART Partnership
A color named Poppy viewed in three different lights (Ultralume, D65, CWF)
How is it different from metamerism?
Shade inconstancy is the change in color of a single sample. Metamerism, on the other hand, is the change in color difference between a pair of samples. Normally, illuminant metamerism is of greatest interest although factors such as observer and geometry can also play a role.
The magnitude of metamerism can be measured by the change in ∆E CMC for a sample pair between any two illuminants. So there are two ∆E CMC values involved. A metameric pair could have a ∆E CMC=0 in one light and a high ∆E CMC in the second light.
Creating shades with a low inconstancy in itself does not improve the chances of getting matches with a low metamerism. It is entirely possible to get high metamerism matches for color constant shades and it is also possible to get nonmetameric matches for color inconstant shades.
Metamerism can only be controlled by using the similar colorants in the color standard and the sample. Attempting to reduce the color inconstancy of a color standard does not in any way reduce the possibility of metamerism.