Below are two photos of a group of yarns, Kertzer Butterfly, purchased from Handknitting.com . It comes in a beautiful range of colors!! It's classified as a DK weight and good for weaving straps.
Look what happens if I edit my photo and put it into black and white mode.
Now I can begin to see the color values rather than the colors themselves. This is a good trick!
Here is one of those beautiful color combinations which really didn't work together in the strap. Oh, if I had only looked at them together in black and white first, I would have seen why. I warped, wove and didn't like it, so I took the whole warp off and added black into the design. It helped, but it is still not a really strong design, in my opinion. If you look at the black and white version, you see that the pretty blue, turquoise and teal are just not different enough to give the design any pop.
In this one, the black and white version shows little value contrast between some of the colors. In fact, some of them completely disappear. But, due to the radical difference of the chartreuse and fuchsia, it still works.
One of the reasons why I think the guitar strap pattern below works so well is that it has high value contrast in addition to having opposites on the color wheel, red and green.
Here are a few helpful resources for learning about colors and their interaction:
http://paletton.com/ Endless hours of fun! Intended for web design, but good anyway.
A Fiber Artist's Guide to Color by Laura Bryant I highly recommend this DVD,
and the 2-minute promo for it is interesting itself.
Joen Wolfrom teaches color interaction in quilting, but gives really good info.
I really like her book, Colorplay.
Also, I just learned that there are glasses with red lenses made just for quilters and fiber artists which help you sort materials by color value. You can buy them here: Nancy's Notions