title: Image diff preserving color for overlaying
body: <p>I have two almost identical images, in color. I want to generate a transparent image that could be overlayed on the first image to make it look like the 2nd. All the image diff tools I've been able to find won't preserve color the way I need. Any ideas? (preferably Linux command-line)</p>
  <p><a href="https://i.stack.imgur.com/QdxU3.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/QdxU3.jpg" alt="diff a" /></a>
  These are the test images I'm currently working with.
  <a href="https://i.stack.imgur.com/oCuM6.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/oCuM6.jpg" alt="diff b" /></a>
  Ideally the result would be something like this, but accurate to the difference. (this one can't add the shadow, and had to be rendered separately)
  <a href="https://i.stack.imgur.com/hjIeX.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/hjIeX.jpg" alt="suboptimal test" /></a></p>