Here is my BCS system. In addition to colors, the data pages allow you to enter insect stage, measurements and colors for just about every part of an insect.
There are regional differences in the color of identical insect hatches, and the color of the insect can change as the hatch progresses from week to week. So precise color matches vary by location and the date of the hatch.
The BCS is no longer sold, but a curious angler can use regular paint chips to do the same task.
Al Caucci and Bob Nastasi published the [u]Fly-tyer's Color Guide[/i] in 1978. The entire book is about the fact the colors are "spectrumized". In the book, they break down the colors in the component parts of red, blue and yellow. They then describe how to get various colors by combining theose three primary colors. They marketed a series of dubbing colors based on this spectrumization but quite frankly it was a bust.