Sure! Here’s an updated color palette that includes the tongue color along with the previous colors:

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

This palette is well-rounded for illustrating a frog monster with a fun and quirky vibe, capturing the essence of the Gravity Falls art style.

Are there any additional features or accessories of the frog monster you’d like to incorporate, such as textures or patterns?