World War II generally had a positive economic impact on African-Americans. There are several reasons for this.
The first is that the economic activity associated with the war generally revived the United States economy through a massive infusion of government money to military projects. This meant a massive growth in job opportunities for all Americans.
Second, African Americans participated in large numbers in the military forces, often quite heroically. Not only was there an immediate impact from military salaries, but it served to reduce racism.
Third, the GI bill enabled many African American to attend university, something that they could not have done otherwise.