Researchers (led by Johnson Chuang from the Simon Fraser University in Canada) have shown that if you choose the color set on an OLED display, you can save up to 40% of the power required.
Different colors in OLED require different power - for example yellow is more efficient than Magenta, at the same brightness.
This can be useful, if you want to get better battery life over display quality. Here's an example of a tooth image:
The left image (tooth) is using standard colors, and the right image is using colors that require 40% less energy on an OLED. The quality is obviously better with standard colors, but almost all the details are preserved. This can be used for applications such as medical or military I guess, where power saving is key.