While black is a traditional color of mourning in Western cultures, I think the decision by AGSM (American Gold Star Mothers) to wear white, rather than black, was a strong statement of how the women wanted to be perceived as they participated in the organization's business. Yes, they mourned their lost children, but white made a symbolic statement that went beyond mourning, a statement of peace, sacrifice, innocence and goodness. Those were the things that their children had been and had died for - wearing white celebrated their children's contributions while the gold star acknowledged their sacrifice.
Image Sources: Adorevintage Pinterest. Article snippet from Gold Star Moms -