Pastel Painter's Pocket Palette: A Practical Visual Guide to Colour Mixing by Rosalind Cuthbert
You can see at a glance how to achieve the colours you want. Just as importantly you can see how to create vibrant effects and learn how to mix and superimpose colours. Four different coloured papers are used as backgrounds to each range and there are over 600 examples to help you create your own palette.
This is a classic book, which was originally published in spiral bound hardback in 1992.