White or black. The bat on the scroll was colored black and the bats on the wall and the moon are left blank/white.
Considering the astronauts were american and the bat was already placed there despite this being the tale of how the Americans won the Space Race, I wonder if the Soviet Union reached space first and left the bat there.
Meaning the black bat would be American and the white bat would be the Soviet Union? Explaining the "Who wins the battle between black and white?" thing Kurusu was going on about.