There are three or four things that help you see in rainbow in the dark:
The Radient Arc, spell summoned archon, SLA summoned archon, and maybe shadowwalk.
I propose expanding that list to include some of the following:
-Summoned fire elemental
-Fire elemental form
-Body of the Sun
-Radient Servant aura
-Hypnotic pattern (?)
-Faerie Fire (lesser radius)
-Wall of Fire
The illumination from some of those could be of a reduced radius, but as it stands, it seems very odd that near-epic characters in a high-magic setting don't have more light sources available.