I'll elaborate. The Blues' cave in the Heaven's Peak swamp, which is surrounded by poison clouds, is not connected to the cave where you find the green minions.
Get the Greens - take your Browns through the Evernight Forest and into their caves; can be a bit confusing to make your way through, but pay attention to detail - then take your newly found Greens to the Blues' cave and clear the way with them.
Unless you're fond of backtracking to swap minions, you'll have to take an increasingly multi-colored horde with you.
Once you're there clean up the mess those zombies made and make your minions stationary at a place while you go ahead and hit the wall two times, to create a bridge. Once that's done go ahead and walk into the cave, clear the poisonous gas first of course, and follow the minions to the hive. Make sure you have at least 20 minions to control first since the hive takes 10 to control (Make sure the blue minion hive is actually carried by blue minions, if you don't have that many blue lifeforces go out of the cave and head on into the lake and kill those ugly birds to get some) and then later on you'll find a gold stash and you'll need 5 minions to carry it. You're also gonna need lots of mana so make sure you save it. At one part you're gonna find a wheel that's surrounded by few ugly birds and the only minions that have access there are the blue ones. You can use the blue's to grab an egg and run away or you can use your spell and burn down all the birds. Once that's done move your minions to the wheel and turn it. When you finished turning the wheel grab three minions and go on ahead and move the stone off of the gayser (or w/e it's spelled).
You're gonna face a huge serpent also in the middle of the cave, you can defeat her by having your browns stand by at your command and using ONLY ONE OF YOUR BLUES to tease it so that the snake tries to snatch him. Once the snake's head is near you send your minions onto it and you attack it as well, once it moves back to its original position recall your minions, but make sure you click as many times as the number of minions you sent in because you don't want to pull the blues in and let them die.
That's basically it, I'm sure you have a guide somewhere on youtube but yeah, this could help a lot too