Take a look at this image on nasa.gov. The text in the image is yellow, the flight paths are white, and Neptune's orbit is green.
When I try to use the SE image uploader to include the image in a question, the colors change, as you can see here:
The text has turned green, the flight paths are blue, and Neptune's orbit is light blue. Every color changed, actually.
When I uploaded the image directly to imgur.com, the colors did not change.
Why is the SE image uploader changing the colors of this image?
Note: This happens for me with Firefox 39 on both Windows XP and Mac OS X 10.7.5. It also happens in Safari 6.0.2 on OS X.