I can understand that they hope to reduce the income gap between different races, but I don't understand why that means the selection criteria should include race.

I would think that it makes more sense to select based on 'wealth' (income, capital, etc.) instead. Since people of colour are disproportionately represented in the poorer population, this would help to reduce the income gap between races (since more people of colour are accepted into the program), without excluding the few white families that could also really benefit from this.