By using dual colorants to compensate for the difficulties of reproducing very light and very dark colors, we also address a phenomenon called hue shifting. This term refers to the characteristic of a color to change its apparent hue as it gets darker. A good example of this concept is a swimming pool. Despite the fact that the water is the same throughout the pool, to an observer, water in the deep end appears much bluer than water in the shallow end, which has an aqua cast and appears shifted toward yellow. This has to do with how light is absorbed and reflected by the greater and lesser volumes of water at each end of the pool.
Light colors tend to hue shift to the yellow, while dark colors hue shift to the blue.
The higher density gives us great dark colors, but it tends to blow away lighter pastel shades, shifting their tones with a noticeable blue component. Conversely, if we decrease the color density of a printed ink, the resulting yellow shift may not be apparent in the lighter tones. But the decreased color strength will definitely show in darker colors, which will appear flat and washed out, with a yellow cast. Two factors combine to cause hue shifting. This is why higher dot percentages display a natural shift in apparent color to blue.