Create a different mixture of colors for your images with the Hue filter. This can be applied by setting the effect parameter to hue (e_hue in URLs). The hue level can be customized.

Here's an original image for example:

Here it is again after applying the hue effect with its default value:

While the default value is 80, you can customize the hue level, for example:

The adjustment of the Hue level is not limited to the main image, it can be changed for overlaid images as well. Here's the same image with an avatar overlay, scaled-down and placed in a 20 pixels offset (for both x and y) from the south-east corner:

Here's the same image after applying the hue effect (with a custom level 50) on the overlay avatar image: