The early twentieth century artist John Sloan wrote a book on art and painting titled The Gist of Art; it is a book which should be in every artist’s permanent art library.
For me the most important chapter in the book is “Painting”; specifically, the sub section labeled “The Color Triangle.” Sloan describes the color triangle as follows:
[He] “found the Dudeen color triangle introduced by Charles A. Winter, a very practical color diagram. The triangle represents color mixtures in pigment form more accurately than does the circle.” [page 119; The Gist of Art]
While the chart from Sloan’s book does not show the full range of pigments available today, it provides the basic information upon which the astute artist can build a representation of his newer palette. One innovation could be to create a similar chart using the color index name number now found on artists’ pigments (you will find a complete guide to these numbers in that indispensable tome The Artists’ Handbook by Ralph Mayer).
My former method of mixing a color was a tedious process of mixing to the exact top color then mixing down with its complement color: a time consuming process which made for very few colors bing put down in a painting session. Now, a series of oranges can be mixed up and down a color chord (e.g., orange to blue which can be understood to be one color) using mars violet and a range between yellow ochre and raw umber: you can see how to mix a color such as mars brown using mars violet and oxide of chromium. The line between two pigments is also a chord.
So, one now can walk into an art store and look at a mixed pigment, such as viridian in acrylics, look at the mixture, purchase the base pigments, go back to your studio, and using the color triangle create the commercial hue and, at the same time, have a greater range of greens.