To create a shadow color for the hex code #319179 (Swamp Green), we can generate a darker variant that can be effectively used for shading and creating depth in your design. Here’s the addition:

 <Frog Monster Shadow Color>
1. Swamp Green - 
                            
                            #319179
                         - A vibrant green reminiscent of the swampy habitats where frogs thrive.
2. Swamp Green Shadow - 
                            
                            #1A4D4D
                         - A deep shadow color that adds dimension and depth, perfect for shading areas of the frog monster.

This Swamp Green Shadow ( #1A4D4D ) provides a darker tone that can effectively create shadow effects on the character, enhancing the overall dimensionality and realism.

Here’s the updated color palette including the shadow color:

 <Frog Monster Theme with Shadows>
1. Swamp Green - 
                            
                            #319179
                         - A vibrant green reminiscent of the swampy habitats where frogs thrive.
2. Swamp Green Shade - 
                            
                            #1E5B4D
                         - A darker shade of swamp green for shading.
3. Swamp Green Shadow - 
                            
                            #1A4D4D
                         - A deep shadow color that adds dimension to the frog monster's body.
4. Mud Brown - 
                            
                            #4B3D27
                         - A deep, earthy brown that reflects the muddy grounds of a bog.
5. Lily Pad - 
                            
                            #A8D8B9
                         - A soft, light green that captures the essence of lily pads floating on water.
6. Monster Eye Yellow - 
                            
                            #E1C300
                         - A bright yellow that evokes the eerie shine of a frog monster's eyes.
7. Pond Water - 
                            
                            #2A6B7E
                         - A cool, dark blue that represents the mysterious depths of a pond.
8. Bug Bite Red - 
                            
                            #D94F3D
                         - A bold red that symbolizes a frog monster's appetite for insects.
9. Night Sky Purple - 
                            
                            #4A2C6D
                         - A deep purple that adds a hint of mystery and night-time ambiance to the palette.
10. Tongue Pink - 
                            
                            #D85E8B
                         - A bright, playful pink that adds a fun and slightly slimy look to the frog monster's tongue.
11. Eye Green - 
                            
                            #A2D600
                         - A vivid and luminous green that adds a captivating pop to the frog monster’s eyes.
12. Lip Red - 
                            
                            #C74B4D
                         - A vibrant and slightly glossy red that adds a bold and playful look to the frog monster's lips.

Would you like to explore different shadow techniques or any specific areas where you want to apply these shadows in your design?