Thing that is green in morning black in noon blue in evening and white at night

The correct answer is: Algae

Explanation:

If you observe the Algae on the sea from the top, you would see this phenomena due to the reflection of the algea, sea-water and the sunlight. As the position of the Sun (during day time) and the Moon (during night time) changes the colour of the Algae also changes, which is why it looks green in morning, black in noon, blue in evening and white at night.