The river is blue. The Eye is blue.
You know, normal life experience things. Maybe some future photographic technique (waaaaaaaaaaaaaaaaay beyond measly 3D) will be able to duplicate these experiences.
This post's theme word is benthic, "of or relating to the bottom of a sea or lake." They Eye's strange, eerie light draws uncanny (Lovecraftian) energy from the benthic depths via the Thames.