And no, the question is not philosophical in nature.
What do blind people see? Do they see black? Well, the short answer is: it depends on the blind person. The assumption that blind people only see black the same way when non-blind people close their eyes is, in truth, the most rare of all the possibilities. What the blind can see depends on the cause of the situation and its severity.
Many who are considered blind can actually perceive light. Even those who need a cane or guide dog when they walk everyday usually see an indistinct fuzzy blur (which is likely both black and white), and not just a formless void. The worse one vision has, the less color he or she can generally perceives.