Yellow/amber lights flashing in clouded night sky.

A very overcast evening, the sun had just set and there were thick clouds on the horizon, low in the sky.  The clouds were concentrated to one area.  
We saw a bright flash with no noise many miles away in the clouds.  It looked like lightning or an explosion in the sky and it lit the clouds with an amber glow.  There were 3 areas where it seemed the flash was occurring.  
It kept flashing repeatedly, around 20 to 30 seconds between each flash.  The longer we watched the more apparent it became that this was not lightning.  
I have no idea what this could have been but there didn't seem to be any red/amber tint to the sky or clouds to explain the amber color of the flash.  
This occurred over a rural wooded area where many oil and gas drilling sites are located and the lights were much too high in the sky to be associated with the drills.