How can I avoid metamerism?
Metamerism cannot be avoided since it is really a property of the human visual system. Metamerism refers to the fact that two colors do not have to be identical in spectral power distribution in order to match in perceived color. You are probably thinking of illuminant metamerism in which two samples match for one light source (a metameric match in which the spectral reflectances differ) and do not match for another light source. The only way to avoid that is to produce spectral matches. (Sorry.
