Colour Confidence in Embroidery by Trish Burr is a must have for any serious embroiderer. The following description was taken from Traditional Stitches:
Based on her own experience with long and short stitch shading (needle painting/thread painting), gained through trial and error over the years, Trish Burr provides a greater awareness of how color affects our embroidery and what brings it to life. Each aspect is clearly illustrated by example and includes tools for selecting colors, choosing shades that enhance our embroidery, why some shades blend better than others, and the importance of contrast with light and shadow. There are projects to represent each color group including stunning roses, camellias, fruit and the birds. However, the highlights of the book have to be the chapters on color combinations and complementary colors. There are more than 200 stitched examples with DMC thread keys.
I knew I couldn't say it any better.
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