This is the list I use…reds in parentheses are for lower-lvl players (approx. 2/3 red):
Ice (blue): 8-1, 8-3, 8-5, 8-7, 9-1, 9-3, 9-5, 9-9, 13-5, 13-8
Fire (red): * (2-2, 5-8, 11-6, 13-1)*…19-4, 19-6, 20-4, 20-7
Nature (green): 6-3, 6-6, 7-5
Holy (yellow): 9-4, 9-7, 10-6, 12-3, 12-9
Dark (purple): 3-4, 4-3, 5-5, 7-4,8-4, 10-4, 11-4, 11-7, 12-5
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I’m going to hop into Rook’s post to add another Dark level. 7-4 is 3 energy and it’s possible to take down 13 dark enemies there. (+2 green bosses if you’re looking to fill monster chests…)
~ Coppersky
Edited again 1/5/19: Red chests now have additional levels in Atlantis (Season 2 map) at 3-4 and 3-8.
Edited again 5/24/19: See link below for good locations to farm color in Atlantis Rises.