I was looking at that color list for what types of enemies you should find on a stage, but it's a little confusing.
The light and dark orange and pink I can pretty much tell.
The dark blue isn't hard either.
But I'm not sure which one is light blue and which is gray.
Is the gray supposed to mean the one that actually looks brown in game?
The Wiki really needed to use screen shots to make the color distinction easier.
Actually, I found that on the page for the Battle Arena, they actually have the colors listed with monster types (more or less) in a picture. So that helps greatly.
Infernal Passage = fiends
Haunted Passage = undead
Mechanized Mile = constructs (although i have seen few that had some weird match ups like beasts)
Wild Path = beasts
Slimeway = slimes
Blast Furnace = fire theme
Cooling Chamber = freeze theme
Power Complex = shock theme
Wasteworks = poison theme
Yeah, I kept trying a stage called Mechanized Mile, but I was getting mostly slimes for some reason.
In-game, you can mouseover the stage icon and determine the enemy type by the stage's name. If you're having trouble telling the colors apart (which is not uncommon), you can figure it out by the name: a clockwork tunnel full of Undead would be "Haunted Passage," whereas one full of constructs would be "Mchanized Mle," I think. (Or maybe Mechanized Mile was Gremlins? But the point is, it's obvious that it's not Undead.)