... re the polariser more saturated and richer colours that is not what one wants when working with original art.
Artists wants the end product to be as close to the original as possible...
Poor choice of words in the original statement. "more saturated and richer colours" is supposed to be in comparison to the image without polarization. In comparison to the original work of art, colors should be close to "as close to the original as possible" after polarization.
However, for artwork, you might want to look into cross-polarizaion, i.e., a combination of polarizing filters in front of lighting sources AND the lens. You can find more by googling, but this article
would be a good start.