Not the OP - I think it's the same process. The difference is in what my inner narrator is doing. When I asleep it is almost always gone, and this is when I typically see things in full color. When awake, my attention is split between listening to its storytelling and the mental imagery, which I believe makes the latter more dull. I noticed that the narrator is more loud when I'm in a minor mental state, like tired or annoyed. When happy/refreshed - there is no voice in my head and I can "see" things very clearly, especially their colors. So, I started looking for ways to divert my attention from the narrator. The most effective seems to keep the narrator busy with commenting on my breath ("in" and "out"), got some boost of mental clarity from that.