Metamerism is the effect of materials appearing to be different colours in different lighting conditions, for example, an extreme case is that cars look different in colour under sodium street lamps than daylight.
A paint related example is that Matt and Silk are two different materials they will exhibit metamerisms at different levels. Under normal electric light and daylight this will not be particularly noticeable and colours appear the same.
Specialist lighting with spectrums designed to highlight specific colours as is often used in retail outlets will exacerbate the problem and the same colour in a different material may appear quite different.