I hopped over to the official Wattstax documentary site and found these amazing images of the festival's fashion.
via WiKi:
The concert was held at the Los Angeles Coliseum on August 20, 1972, and organized by Memphis's Stax Records to commemorate the seventh anniversary of the Watts riots. Wattstax was seen by some as "the Afro-American answer to Woodstock". To enable as many members of the black community in L.A. to attend as possible, tickets were sold for only $1.00 each. The Reverend Jesse Jackson gave the invocation, which included his "I Am - Somebody" poem, which was recited in a call and response with the assembled stadium crowd. In the film, interspersed between songs are interviews with Richard Pryor, Ted Lange and others who discuss the black experience in America.