There are many barriers that prevent business owned by black women from making as much as those owned by black men, and a new report from the National Women's Business Council, prepared by Walker's Legacy, highlights the most pertinent. But even among the handful highlighted by the report--including a lack of mentors, discrimination, and a lack of adequate networks--one in particular stands out: access to capital.

Overall, black women are uncommonly entrepreneurial, and it's women of color, in general, who have been powering the growth in new businesses. Black women own 58.9 percent of all black-owned businesses, and among the demographic groups listed by U.S. Census' Survey of Business Owners, blacks are the only ethnic group within which women own more businesses than men.

But businesses owned by black women, just like those owned by women of other races, bring in less money than those of men in their same demographic group, and businesses owned by blacks have lower revenues than those owned by whites. The average black-owned business has revenues of $58,119; the average white-owned business has revenues of $552,079. The average business owned by a black woman has revenues of $69,101, while the average business owned by a white woman brings in nearly three times as much -- $189,037.

The difficulty in getting money to fund those businesses begins early -- long before potential venture capitalists, or even bankers, would get involved. The median net worth for a black family in 2011 was only about $7,111, according to the report, compared to $111,146 for a white, non-Hispanic family and $8,348 for a Hispanic household. The report describes this as "a lack of generational wealth and limited present and historic assets." The report says it would take the average black family 288 years to amass the same wealth as the average white household.

Given that most Americans do not have strong social networks that cross racial lines, that makes it almost incomparably harder for a black woman entrepreneur to raise a friends-and-family round than it would be for a white woman entrepreneur.

Income figures also show a dramatic disparity. As of 2014, according to the report, the average household income for black households was $35,398. This compares with $42,491 for Hispanics of any race, and $60,256 for white non-Hispanics.

Bank financing is not always doled out equitably, either, according to the report. Yes, there are some minority and women entrepreneurs who do not apply for bank loans for fear they'd be turned down. But at least part of that fear seems to be entirely rational. A 2013 report from the Small Business Administration found that even when the type of business, business structure, and credit score were the same, women- and minority-owned businesses were less likely to get approved for loans.

The report makes several recommendations that would help enable black women entrepreneurs to get the funding they need. One is for those women to seek out nontraditional and alternative funding sources, such as loans from Community Development Financial Institutions and microloans. Another is continued and increased support for community-based business resources such as Minority Business Development Centers, Women's Business Development Centers, and Small Business Development Centers.

Lastly, since investors tend to back people who look like themselves, the report urges the creation of more angel investors who are also people of color. Given the low levels of wealth among families of color, that will no doubt be a continuing challenge.