The Feeling blue achievement is worth 30G and can be unlocked by staying in one True Blue for 30 seconds.

To go into True Blue mode you will have to free the animals in the game and collect the blue tubes that spawn after you've freed the animal. To stay in True Blue mode you must keep freeing animals and collecting the blue tubes. This can easily be done in level 1-1. You will be at a section where there are a bunch of animal very close to each other. If you get hit you will lose your True Blue.