Why not? He has always considered what his images mean. Anakin's shadow casting a form of Vader is not even subtle. It was in the marketing for TPM. Anakin being shrouded in darkness is not subtle. These are very basic visual cues from Lucas. This goes back to his film school days. He plays with this imagery in all his work. Lighting and color mean a lot to Lucas. He started in still photography, not film, so composition and lighting are things he seriously considers.
I'm not sure why people downplay Lucas' visual language. Other directors don't. Listen to Dave Filoni talk about Lucas and how he works.
Here is a
clip with Lucas talking about the importance of visual literacy. It also helps explain why his dialogue is the way it is, he values visuals more than spoken language when communicating ideas