White--representing air or wind
She discussed the fact that the flags are called "Wind Horses," and that the belief is that every time the wind moves the flag, it send the energy and prayers contained in the flag, not to a divine being, but through the space, blessing everyone. So it is a belief practice much in line with the Buddhist tradition of universal connection and compassion.
Reverend Belt helped the students create universal healing prayers involving all of the different elements. They they wrote those prayers on their flags, sometimes also decorating them with a horse image or other decorative elements.
Once they were completed, the teachers demonstrated the traditional way to hang a set of prayer flags...
It can be a very powerful--and beautiful--way to talk about Buddhist beliefs.