For starters, something capable of standing up to sudden extreme changes in size. Sharla Shenanigans necessitate it... Clarabelle will be walking down the street then WHAM!! Asscheeks the size of cars.

As for colors and patterns...
Maple- Pink
Clarabelle- Plain white (I have been debating different patterns...)
Victoria- Green
GG- Still on the fence if she does, tbh... I mean, what would it cover? She doesn't have a (regular) digestive or reproductive system
Sharla- colored like missing textures (purple and black checkerboard)
Freya- Purple and white stripes
Ysabel- Black (only a bra, I don't know how a lamia would wear panties)
Tabitha- White. White and frilly...
Jules- ???
Astrid- ??? (Often forgets a bra though...)
Yuzu- ???

Antares- Same as GG