I wanted the leotards to result in an overall monochromatic feel to Sarah and Nanase. With that in mind, I actually went with analogous color schemes with the leotard hues effectively being between the hues of their skin and hair colors.
I'm happier with my choice of background color here than in previous color experiments involving this... Dungeon? Crypt? Wherever the heck they are. It looks a bit more natural to me, though experimentation with such things will naturally continue.