Asked and answered, blue: Just use GIMP / Photoshop / Painter, whatever fits your bill 🙂
Changing eye color isn’t possible because the eyes arent at the same place depending on the type of eye you pick for your character so it’s nightmarish to code.
It was easy for the first version of ePic because the eyes were the same for all characters and they didn’t move. 🙂
So well, just use your favorite image editor select the irises and adjust hue/saturation/luminance or something like that 😉