foamy ATF

I started my truck cold, drove it around normally for about 15 mins until the engine got to op temp, and parked level on the street.
I put the transmission in each gear for a few seconds to get the fluid circulating and then left it running in neutral while I checked the level.
The level is good, but there was a fair amount of foam on the stick. Wiped clean and rechecked, same thing. Check one more time and still foam.
What causes this? The fluid didnt smell burned, actuall it didnt have a smell....wierd. It was slightly brown, not that deep red it should be. There was also a pasty residue about an inch up the stick above the top of the fluid also, but Im really concerened with the bubbles.............