When it comes to color schemes, I have a weakness. I'm really partial to monochromatic and analogous color schemes, that is shades of one color or colors adjacent on the color wheel. This can look really great in stripes, but presents problems with smaller patterns like fair-isle motifs. I was planning to use these two yarns for my sister's Center Square hat.
However, when I started making the hat, it was almost impossible to tell the MC and CC apart. My brother's girlfriend described the look as "noise" rather than a discernible pattern. This is not really the point of colorwork, now is it?
The solution: contrast. I hit on it this summer when I paired a blue and white variegated yarn with another blue yarn for my first attempt at the Mad for Fair Isle Batik Style socks. It looked good from a viewing distance of a few centimeters, but you couldn't even see the pattern any further back. Then, I switched my main color from blue and white to a pink and orange variegated.
Ta da! The contrast makes the pattern visible. Or would, if my picture was bigger. (Trust me, they look great) A quick perusal of my Ravelry page shows me that all of my surviving color patterns (except one) have really bold internal contrast. Of course, don't follow any rule off a cliff. (It would happen that I can't find the example I was looking for. poot) Anyway, I hope that articulating this rule will help me follow it better in the future. Less frogging that way.