Color Palette:

1. Color Name: Earth Green
   Hex Code: 
          
          #006400
       
   Description: This deep, rich green represents the lush foliage and natural beauty of the Earth. It symbolizes growth, harmony, and the importance of preserving our planet.

2. Color Name: Sky Blue
   Hex Code: 
          
          #87CEEB
       
   Description: This light, serene blue shade resembles the clear sky on a bright day. It signifies purity, tranquility, and the vastness of our atmosphere.

3. Color Name: Sunshine Yellow
   Hex Code: 
          
          #FDB813
       
   Description: This vibrant, energetic yellow captures the warmth and radiance of the sun. It represents optimism, happiness, and the essential role of sunlight in sustaining life.

4. Color Name: Ocean Blue
   Hex Code: 
          
          #0077BE
       
   Description: This deep, captivating blue shade mirrors the depths of the ocean. It signifies the vastness and mystery of marine ecosystems, as well as the importance of water conservation.

5. Color Name: Earth Brown
   Hex Code: 
          
          #8B4513
       
   Description: This warm, earthy brown color reflects the natural tones found in soil, representing stability, grounding, and the foundation of life on Earth.

6. Color Name: Leafy Green
   Hex Code: 
          
          #228B22
       
   Description: This fresh, vibrant green shade evokes images of lush foliage and growing plants. It symbolizes renewal, vitality, and the importance of sustainable practices to protect our environment.

This color palette for an Earth Day social media poster incorporates shades of green, blue, yellow, and brown to represent the beauty and interconnectedness of our planet's ecosystems.