Why can two colors match under one light source but not match under a different light source?
This is a common color-matching problem and it is caused by Metamerism. Because colors can be created by using different mixtures of pigments and dyes, the combination of dyes or pigments used will determine how well colors match under different light sources. The greatest effect of metamerism can be seen when viewing a sample under a predominantly Blue source (e.g., D65) and a predominantly Red/Yellow source (e.g., Illuminant A). If the same dyes are used, no metamerism should be seen. If different dyes are used to create the same color, metamerism is possible. When comparing different samples, one colored using dyes and one colored using pigments (evaluating a textile sample next to a paint sample for instance), metamerism is not uncommon. Finding the right “mix” of dyes and pigments is part of the color technologists job. Sometimes, metamerism cannot be eliminated completely, only reduced.
