** These charts were added to the 2021 Printing of Mark's "BASIC COLOR PENCIL" Book.  So if you purchased a 2021 edition after November 1, 2020 Your do not need to purchase this set as they are already included in the book.
Selecting Prismacolor Color Pencils by QUADRATONES 
    To help you master the four value approach, I have created the QUADRATONE reference charts, each with a number of differing combinations. For example, I have listed a BASIC QUADRATONE for general use; other selections on each chart include INTENSE; WARM; COOL; SUBTLE; and GREY. I have also included the tertiary colors related to a particular category. For example, in the RED category, I have included VIOLET-RED and ORANGE-RED selections. Please note, the VIOLET, YELLOW, EARTH and GREY charts have fewer choices. A few of the combinations use colors outside of the color category
    The set of 8 color charts are designed to initiate you to the method of color selection and to simplify your efforts. These combinations are not intended to be the only value combinations you will ever use. As you practice the four value approach, my hope is that you will eventually create your own personal QUADRATONES combinations, derived from keen observation.