Merchants seem to believe white people don't buy things anymore. Blacks are featured on nearly every page of advertisements for clothing. In Barry's world, we are the minority as are hispanics and asians.
By the ads it puts out, I’d say my bank thinks only light-skinned black women between the ages of 30 and 40 do any banking.
I live in a 98.5% white area. Yet, the wall ads in Walmart show blacks. The hair care aisle has a Black hair section.
I have noticed the same trend in national ads that you note. Blacks and Hispanics predominate, with a scattering of Asians and mixed race and a token white or maybe two, usually only one of them blonde.
They must do studies and I conclude that those studies do show that non-whites buy more. We are constrained by high taxes, lack of government benefits and an aversion to debt. It is probably accurate that whites spend less, proportionally.