Atmospheric distortion sounds like the best answer to me. The Black Omen could be said to cause a lot of distortion itself, so let's just chalk it up to that.
A lunar eclipse, on the other hand, doesn't seem that likely. For one thing, there's no shadow on the moon. Granted, it is possible for the shadow to be close enough that atmospheric filtering would occur, but then there would be a definite gradient. Besides, the only reason we see orange during an eclipse is the pollution in earth's atmosphere; it would appear yellow if the atmosphere were clean. Pollution is also the reason sunsets/sunrises are so beautiful; think about this next time you admire one.