Here's how it's used:
* The fish itself is described as "green, and very old, and very tired". This establishes the fish's age and weariness, hinting at a long life of struggles and challenges.
* The "green" seaweed is mentioned multiple times, further emphasizing the connection between the fish and the sea. This suggests the fish is a creature of the deep, fully integrated into its environment.
* The "green" line and the "green" net symbolize the entanglement and struggle of the fish. This highlights the dangers of the ocean and the relentless fight for survival.
The repetition of "green" throughout the poem acts as a motif, drawing attention to the connection between the fish, the ocean, and the theme of resilience in the face of adversity.