Here are a couple good pictures to compare to your ball python...
http://siscoreptiles.com/ball%20pythons/YB%20(1).jpg
http://siscoreptiles.com/ball%20pythons/YB%20(2).jpg
Here is a list of what I look for in a good yellow belly...
- The spot on the head
- The clear belly
- The pixelated markings where the belly meets the sides
- The awesome flames on the sides
- I also love to see a little yellow on the outer belly scales
Rick