FOUND IT!
You stare into the abyss once more. Almost every time you blink, one of the colorful lights flickers out, erased from history forever. You stand like this for some minutes before snapping back to reality.
Slog was off the traveler's sack. Slog was off the traveler. Slog was off everything he knew, falling through a crackling void without end. He felt a wincing pain in his center: a small, all-present hand pulling something precious, something important out from him. A brief light shone in front of him. It was beautiful, simplistic. It was Slog. It was everything Slog was! Every emotion he'd ever felt, every blorb he'd ever orbled, every adolescent Red Slime to ever turn him down. Slog smiled for a second, and it was gone.
Guys... I feel so stupid....
The Multicolored lights in the void were Souls all along, and Slog had the answer.
We were entranced. Slog was entranced.
The light of a Soul, the representation of everything a person is and has been.
So now we have the proper evidence to state that the Multicolored Lights in the Void were Soul Stars.(at one point)
Slog's Backstory states he had seen the Light of "Everything he Ever Was", then it was taken away from him; just like the Lights in the Void, which:
You stare into the abyss once more. Almost every time you blink, one of the colorful lights flickers out, erased from history forever. You stand like this for some minutes before snapping back to reality.
Disappear forever. Because they were drained of Soul Charge. Left as "unallocated" husks.
^What happens after Entering the Warrens.
Starting the process of Illbirth, where the Soul is drained, and leftovers discarded, in the Void.
Also, Soul Stars are colorful, we've seen teal, red, brown/orange, Pink, purple, green, Yaos Purple. All the colors.
So the Lights we see, are the newly created Soul Stars of imminent-Illborn, which then disappear later due to being unceremoniously drained of all their power.