iMovie changes not "sticking" when uploading to YouTube

I fixed the color and sound on a video in iMovie, exported it to my computer, then uploaded the file to YouTube, but the changes I had made were no longer there! The .mp4 file looked fine in QuickTime, but on YouTube the color was all wrong again. I exported the .mp4 to an .mov file in QuickTime and then uploaded that, but the same thing happened.

Any idea what's causing this, and how I can fix it?