Sepia

Sepia \SEE-pee-uh\ , noun;
1. A brown pigment obtained from the ink-like secretion of various cuttlefish and used with brush or pen in drawing
2. Photography: A print or photograph made in this color
3. Any of the several cuttlefish of the genus Sepia, producing a dark fluid used naturally for defense and, by humans, in ink
adjective;
1. Of a brown, grayish brown, or olive brown similar to that of sepia ink

I, for one, had no idea that sepia had anything to do with ink, let alone fish. I assumed that it was just the way photographs where printed back in the day. Well, you know what they say about assumptions...

Sepia comes from Italian seppia ("cuttlefish"). The pigment meaning is first attested in 1821, though the cuttlefish meaning dates to the 1560's. Seppia derives from Latin sepia ("cuttlefish"), which was borrowed from Greek sepein ("to make rotten"). Sepein is, perhaps unsurprisingly, the forebear of sepsis.

Cuttlefish in sepia...see what I did there? (credit)