Spectrum colors in paint

An artist friend queried a watercolor group today about what the term "spectrum" means when it's used in a paint name. Here's my reply: "Spectrum" colors in paint are a myth. You can't have spectral color except in light. This is one company's idea of a "true" color, whatever that is. The same is true of colors labeled "primary" this or that. What's primary? If you collected them all and compared them you'd realize there is no standard in paint and the terms are meaningless. Best to stick with pigment names and numbers. Even then, you'll find that some paints with the same name and number vary widely from brand to brand. He responded that he had found that Raw Sienna in M. Graham and Cotman are very different and he had a definite preference for one over the other. Artists need to make such comparisons themselves and not assume that another brand will be the same as the one they prefer. Manufacturers' printed paint charts aren't much help. Colored inks don't do a very good job of reproducing paint colors. If a painted chart is available, you can see the actual color and judge your colors better.