Oh yes, a Pantone (PMS) color match number would be great..........looking to repaint a full size piece of rolling stock and want to get it right.

You're only in love with that Pantone because it's the only color matching system you've ever heard of.

It matters because of metamerism, as Dennis discusses. This is why things that match outside don't match inside... It's why screen colors don't match printed colors. It's why model railroad paints are not suitable for the prototype. It's why your hardware store's paint carousel has a dozen plus pigments instead of just RGB. It's why printing with an ink system (CMYK) doesn't fit or match up to real paints.

There is a basic incompatibility between print and paint.

The problem with Pantone, particularly, is that it is made for the printing world, not the painting world. First, it's a curated system - staff choose only certain colors to be made available. It is curated for graphic arts and media design, principally on paper, to help graphic design companies successfully market. It's all about the pitch meeting in front of the clients. Pantone is optimized to get you to *choose* a Pantone color as your choice, the system is not designed to match a color you already have. In fact Scotland changed their flag to make their blue a specific Pantone number. That's what Pantone makes you do, this is great for lock-in. Nobody at Pantone could give a damn about Pullman green. That is a color that won't reproduce well in print, anyway.

On the other side of the aisle (literally) is Munsell and other spectra based systems. These are designed for identifying and matching the color you already have. They define a color in three factors: the hue, the lightness, and the saturation. Which are physical characteristics. A such, a Munsell number can be derived from any color. And the system is designed to help you do that.

Munsell in particular developed into a company of some reknown, particularly in the 30s through 50s: they were the Pantone of their day. They publish a large swatch book with 1600 swatches and one hue per page, in a grid: lightness up and down, and saturation left and right. As such, it's rather easy to zero in, especially since you can evaluate each one on its own axis: figure out lightness first, then hue, then saturation. And they make it easy to interpolate: so if your lightness is halfway between 6 and 7, you can see that and express that in the code by just putting 6.5. And even measure it with an instrument and discover that it is in fact 6.41.

As opposed to matching out of a Pantone book, where it's a disaster, you might as well use hardware store paint chips. The book is organized for graphic artists to help clients pick complementary colors. And so colors are arranged all bric-a-brac based on how they complement each other, not based on their physical values. If you tried to rearrange your Pantone book in hue/lightness/saturation, you would end up with clumps and holes, because like I say, Pantone is a curated system by and for graphic artists, and it is confined to colors which a graphic artist would want to deal with trying to render in a variety of media while the client breathes down his neck.

Relevant to our interests: before Pantone, the dominant swatch book in the world was Munsell. And more than one railroad, rather than work with fractional in-between colors just picked a swatch out of the Munsell book: "That one will suffice, 5BG 7/4". And then 60 years later, you pleasantly discover your historic fabric is not *between* swatches, it *is* a swatch. No interpolation required.

Metamerism impacts because Pantone lives in a CMYK world which depends very heavily on metamerism to make colors look right. Spectral systems much less so, since they are after the spectra. Munsell is a system specifically designed to work in paint. (At the time, color printing was not ubiquitous, so paint was the market; as that changed, Pantone won because it is curated, and so, easier for graphic designers to work with.)

Pantone is designed to work with Pantone brand inks. (As in inks print shops buy by the gallon). Again, marketing lock-in.

Ironically, Munsell and Pantone are literally across the aisle, both owned by XRite, in Grand Rapids, Michigan. XRite is also the main manufacturer of hardware store paint scanners.

Glad Pantone inks were mentioned. The main purpose of Pantone swatch books is to give the printer the CMYK formula after the graphics design people pick the colors out of the swatch book. I actually bought a Pantone book years ago (not cheap) specifically with the thought of using it as an intermediate match between actual railroad equipment and model paint; absolutely worthless. There are not enough colors.

In our files at work (Accurail) I have a set of TTX Co. color chips we acquired somewhere, that were prepared by the Munsell Co. Each file card size chip is marked with the color name, Munsell notation, Munsell part number (I assume so one can re-order the chips) and a paint specification number without further explanation. Munsell has been around long enough to have been doing this sort of work during the colorful "streamliner" era. I wonder if they have some of these colors on file?