Found the left image from iFanboy and the other is my edit from comicaddicts.com
In his commentary in The Killing Joke Deluxe Edition Brian Bolland mentioned how John Higgins original coloring doesn’t really match what he was aiming for and he asked to recolor it when they make the deluxe edition.
Yeaaaah… I can see why. There’s a lot of unnecessary color here, and it’s too saturated. I guess he was going for the crazy mood of the story, while Bolland’s going for realism and the melancholy and tragedy of the story. Personally Bolland’s subdued, more realistic coloring works way better for me.