1. So you just scanned your image, the colors look like shit, because scanners aren't a magical piece of machinery like in the movies and don't scan exactly what is in front of you.
2. Either go to Image > Adjustements > Levels or hotkey: Apple + L (Mac), or Ctrl +L (PC)
This should be what comes up, make sure preview is selected.
3. Open "Options..."
This is what you should see next.
4. Under Algorithms, click the 3rd option, "Find Dark & Light Colors", then hit ok.
If you have preview selected, it should show you right away. I used it for all of my scans yesterday with my paintings and it was perfect everytime. I have no idea what the other options on this window do, but I'm assuming if you have a one color image the 1st option would work well...play around. I'm going to need this when I scan Mini Battle Men #2 this week.