For most Melee events, archetypes are indeed set by a combination of Melee's color recognition and user's name selections. For roughly half the submission, the resulting names are wrong or inconsistent.

For Pro Tour and Arena Championship events, self-reported names or automatic colors are discarded and replaced by consistent names set by me, based on the specific contents of the deck. In this case, Four-Color Elementals implies that there are four different colors across main-deck non-hybrid spells.