I believe all yarn manufactures should publish a Color Coordinates Chart that would help consumers match their brand of solid color yarns with their variegated yarns.
Red Heart Yarn has already done this. To use Red Hearts Multi-Color Coordinate List
You can find a PDF file here.
The List was designed to help coordinate their solid colors with the variegated or multi color yarns. But you can also use it to choose colors that blend together even if you are not using a variegated yarn. Just pick a variegated yarn that has the colors you want in your project that then check the list see what blends with it. How simple is that ?
Of course that does not mean you still cannot throw in a color or two of your own choice as you can see from the Purple I added to this one. I do tend to get carried away sometimes.
I have recently had email contact with a representative in Caron Yarn's Customer Service Department and she told me she would forward the Color Coordinate List suggestion to their board. Let's hope Caron will publish A multi-Color chart and other yarn companies will do the same. .