Answer:
Your eyes are as dark as a sky without stars.
Step-by-step explanation:
A metaphor is used to describe an action or an object in a way that is not true but help us to understand the idea that someone is trying to explain with its use.
When we compare someone's eyes with the sky saying for example -your eyes are as bright as the full moon- we know that this is not true but as we are trying to describe his or her eyes with a metaphor we are emphasizing a characteristic about a person that is easy to understand due to common knowledge ( everybody knows that the moon is bright ).