This effect was generated in Filter Forge, a Photoshop plugin that allows you to create your own filters.
This is a simple filter that split your image into half 1 color and the other half another color, you can also desaturate or saturate it too. You can control the positions of the halfs, add a dividing line and change its color and thickness.
double, color, half, colour, desaturate
This filter has earned its author one of our rewards. They are given to the authors of popular filters and include a free copy of Filter Forge.