Here is the full list of all 22 ChromaGun achievements.
Finish Chapter 4.
Try jumping over a Deadly Electrified Maintenance Tile... and fail horribly.
Find the hidden cake we actually have, as opposed to that other game that doesn't have a cake.
Finish Chapter 3.
Try painting a brown WokerDroid and realize how pointless that was.
Grill a WorkerDroid on a Deadly Electrified Maintenance Tile.
Simply walk onto the Deadly Electrified Maintenance tile in Chamber 3-1.
Finish Chapter 2.
Get killed by a WorkerDroid.
Mix a color. It's not that hard, really.
Finish Chapter 1.
Fire 100 shots.
Open a door by activating a trigger.
Try jumping... and fail.
Shoot a WorkerDroid.
Grill 100 WorkerDroids on Deadly Maintenance Tiles.
Finish Chapter 5.
Finish Chapter 6.
Finish Chapter 7.
Finish Chapter 8.
Solve a chamber in chapter 7 without firing a single shot.
Rescue the WorkerDroid in Chamber 5-2.