If we were on the moon during a lunar eclipse, the Earth would be backlit, and everywhere along its edge is at either sunset or at sunrise. The sky there is familiar to us: red and orange, the colors refracted slightly around the Earth’s edge by the air. It is this reddish-orange light source that illuminates the moon when the sun no longer hits it directly.
This picture was taken during the midpoint of the eclipse when the moon was deepest in shadow. The “bottom” of the moon is brighter. This means that the moon didn’t pass through the dead center of the Earth’s shadow, but toward one side. The visual appearance was a dim grayish brown, but a long enough exposure on film shows the red component to its color.