Sounds like it might be the Green Flash to me. That's an effect where the atmosphere acts as a prism, and bends part of the sun's light enough to be seen when the body of the sun's just beneath the horizon. Like a prism, the amount of bend depends on the frequency of the light, so the flash is typically green or blue/green as these are the components that are bent the most.
I've only heard of this happening at sunset, but can't see any reason why it wouldn't happen at dawn. If you're at altitude, then you'll have a better chance of seeing it than if you're on the ground.
A good discussion of the effect is at
http://www.mtwilson.edu/Tour/Lot/Green_Flash/
Does that sound like it matches your observations?
R