Answer:
Step-by-step explanation:
It depends on the era. If you mean the Black Panthers the dress was more militaristic and it suggested opposition to Vietnam. If the reference is to something earlier (like Martin Luther King), then the emphasis was on dignity and correctness. There's a wonderful picture that you can find of this era where the people marching (most if not all men) wore dark suite and striding at the front is a woman wearing all white. She's not a contrast. She's more of an emphasis to the men all dressed in white shirts and ties.
Fashion has always been a statement about protest. You have to look the part.