Pantone makes something called a GoeGuide:
http://www.pantone.com/pages/pantone...?pg=20467&ca=1
Looks like the ultimate color matching system... or, at least, good enough for my purposes. With 2058 that ought to allow me to define fabric colors pretty well.
From what I've read, it has numbers that correspond to CMYK (cyan-magenta-yellow-black) pigments, for printing, and also they have RGB (red-green-blue) numbers that correspond to colors on a computer screen. (YES!)
And they make these color fans on glossy paper, and flat. I'm assuming that to match cloth, flat would be better.
They make color swatches on cloth, too but to buy that would cost THOUSANDS of dollars. The paper version is under $200.