Suppose there was a spherical red light source and that was the only thing that existed. Would your eye see a red ball surrounded by blackness, or would your whole vision be uniformly red, or would you see all red but in decreasing intensity?
In case you haven't- When you look at the stars at night you see bright lights surrounded by blackness. (Works best far away from city lights- spend a night in the Utah desert some time- it's awesome!)
You would only see "all red but in decreasing intensity" if there were a cloud of something to reflect the light around the source.