Color Palette for Fantasy Koi Illustration:

1. Color Name: Azure Mist
   Hex Code: 
                            
                            #7CC5D9
                        
   Palette Description: A refreshing light blue reminiscent of a calm and serene pond, perfect for representing the tranquil waters where the fantasy koi swim.

2. Color Name: Sakura Petal
   Hex Code: 
                            
                            #F8B7C7
                        
   Palette Description: This delicate pink hue captures the essence of cherry blossoms, evoking a sense of grace and beauty. It can be used to add a touch of femininity to the fantasy koi illustration.

3. Color Name: Dragon Scale
   Hex Code: 
                            
                            #2F4E4C
                        
   Palette Description: A deep, mysterious green with hints of teal, resembling the shimmering scales of a mythical dragon. This color adds intrigue and a touch of magic to the illustration.

4. Color Name: Golden Sun
   Hex Code: 
                            
                            #FFD700
                        
   Palette Description: A vibrant, warm gold color that represents sunlight reflecting off the scales of the fantasy koi. This shade brings a sense of radiance and majesty to the artwork.

5. Color Name: Coral Reef
   Hex Code: 
                            
                            #FF7F50
                        
   Palette Description: This vibrant orange shade captures the vibrant colors of coral reefs. It can be used to add energy and vibrancy to the illustration, depicting the lively environment where the fantasy koi reside.

6. Color Name: Moonlit Night
   Hex Code: 
                            
                            #3F3C4A
                        
   Palette Description: A rich, dark indigo color resembling the night sky. It represents the calmness and stillness of the nighttime, providing a backdrop for the fantasy koi to shine and stand out.

Note: Feel free to adjust the shades or explore different variations within the color families to suit your specific illustration style and preferences.