The American Brahman (both Gray and Red) was developed from a mixing of Indian and Brazilian breeds (Gir, Guzerate, Nelore and later the Indu-Brazil) imported into the U.S. and Texas from the mid 1800's until 1946
The Gray have more Guzerate blood and the Reds have more Gir. The Grays start off reddish or with a reddish poll from their Guzerate heritage. Temperments are a bit different between the reds and grays the reds being more complacent and easier to handle. The gray is a shorter meatier animal and is the most popular type. I perfer the red mainly for the temperment.