the.com/tortoiseshell

means A mottled coat pattern of orange (or cream) and black patches, named for its resemblance to the actual shell of certain tortoises — most famously seen in cats, almost always female.

from The word is simply 'tortoise' plus 'shell,' first used for the real mottled shell of sea turtles (especially the hawksbill) once prized for combs, buttons, and ornaments. 'Tortoise' itself traces back through French and Late Latin, of murky further origin — possibly tangled up with 'Tartarus,' the classical underworld, from old associations of tortoises with darkness or the infernal. The cat-coat sense came later, borrowing the shell's blotchy orange-and-black look as a ready-made name for the pattern.