Color of the toads has almost nothing to do with the sexes. Males usually are smaller than the female when full grown and have bumpier skin. If you take a few moments to look at the toad's digits, the webbing will either be about 75% up the digits (toes)- which indicates a male, or about 25%-30% - females. Occasionally, you will see one of the toads on top of the other. On top is usually the male, and bottem, female. If they are both males, then they might also 'wrestle' each other_ grab a hold of each other similar to sumo wrestling. I have a video explaining further: How to: How to Identify Fire Belly Toad Gender - YouTube
Hope this helps
-Shawn