It took me a while to come up with an idea for this since the challenge was to represent an object with it's complementary color while having its background possess its original color.  I wanted to have a background that was more interesting than just a flat color, and I wanted the colors of the image to make sense, and not just be an image with strange colors.  I eventually came up with the idea for the original color to be blue so that the background would make sense as a nighttime sky with the orange representing moonlight on the object (so the challenge's color change would make the original scene go from day to night).

 

So the scene became a landscape with some sort of water to be the object in question.  Instead of a lake or ocean, I went with a river so I could have the sides be a different color to reduce the contrast in the image and balance it out a bit.  Early on I figured the best way to get another color into the image to make it more interesting would be to use brown since mixing a color with its complement gives a form of brown, and I could use this between the object and the background to have the foreground color "mix" with the background.

 

It was pretty fun, and I think I got some ideas for using more pure grays in general...  Though I'm still terrible at clouds -_-.