You may select from four categories: red eco, yellow eco, blue eco, and green eco. There are no dark eco or light eco powers, unlike in the game's predecessors, thus there are no corresponding skills available. Each skill in a given category is unlocked sequentially, meaning you must purchase them in order of appearance, each increasing in cost as you progress (though you can select from any of the categories as you please). Once unlocked, the skills are free to use and expend eco from neither the dark eco meter nor the eco power meter.