Only 7.6% of the population is black. 43.1% is "mixed" and 47.7% are white (2010 census). Point being simply that you wouldn't expect to look at any crowd of Brazilians and conclude that the "average color" (made up concept) is black. I think that is something not even Brazilians are fully aware of, this country simply isn't that dark skinned on average.
As far as the tickets, its a product in very high demand, consting a fair amount of money. Even when considering discounted prices the process of actually buying a ticket is not so simple where I would expect someone not very educated and not travelled at all to be able to actually get one, even if he has the money. Buying tickets for your regular matches here, even say a Libertadores final, is a matter of queing extra early outsides the stadium or the club to eventually hand over cash to get a ticket (not nominal, no specific seats, etc.).
Buying a WC ticket has been a fully online process, requiring a credit card, a basic undestanding of how such a website is organized, etc.
But isnt this to be expected even at a WC in Europe? Most tickets taken by people with higher disposable income and a higher level of education? The only great difference in that in Brazil not being educated or having just high school is a lower baseline than the European equivalent.
Edit: Sorry, hadn't seen
Maksimilian had posted the same census data.