Use of "de" vs. "des"

Question

Why "s'illumine de lumieres colorees" and not "des lumieres colorees"?

I understand that "des" becomes "de" when the adjective precedes the noun that it is modifying, but in this case "colorees" is after "lumieres".

Accepted Answer

Bonjour N. Hilary,
La ville s'illumine de lumières colorées -> "de" because there is no complement to "the colourful lights" 
La façade s'illumine des lumières colorées du grand projecteur = the wall is illuminated by the colourful lights of the big projector
-> "des" because there is a complement associated to the colourful lights making them precise / specific
@Chris, La forêt s'illumine de la lune isn't possible in French. You cannot use "s'illuminer" to express the passive voice here. Instead, you will use the following: La forêt est iluminée par la lune.
I hope this is helpful.
Bonne journée !

Answer

La forêt s'illumine de la lune. -- The forest is illuminated by the moon.
The preposition de is used in a causal sense in this sentence, not a partitive one.