Step 1: Understanding the Concept
This question asks to identify a "cool" colour from the given options. As explained previously, colours are categorized as warm or cool.
Step 2: Detailed Explanation
Cool colours are typically blues, greens, and violets. They are associated with water, sky, and nature, and often have a calming effect.
Warm colours are reds, oranges, and yellows. They are associated with the sun and fire and tend to be energizing.
Among the options, Orange, Red, and Yellow are all warm colours. Green is the only cool colour in the list.
Step 3: Final Answer
Therefore, Green is the cool colour.