Nice! It seems to work OK for an image I uploaded.
One thing that is not clear to me is the "complementary color": the code of the complementary color is displayed, but I can't see what color it is. Or am I missing something? It would be nice if the complementary color could be displayed in a box, like the dominant color. Or is it the background color of the page?
What I think would be really great too, is if the application could suggest a color palette instead of two colors.
Something else I'd like to see is some tips on how two use these colors when designing a web site.
Hope this helps!