Avoid Adjacent Colors Differing Only in Hue
Color combinations that vary only in hue produce another kind of "washing",
whether or not the colors are of low value (again, see "negative" button below). The reason for this is that the edge of any region is perceived primarily through brightness gradients. To be seen distinctly, boundaries should vary in value as well as in hue. The color blue, it should be noted, is idiosyncratic in this respect: it contributes little to the perception of brightness, and boundaries relying entirely on shades of blue will remainm indistinct.