'Lieutenant Sandridge turned a beautiful couleur de rose through his ordinary strawberry complexion, tucked the letter in his hip pocket, and chewed off the ends of his gamboge moustache."

I posted about this not long ago, but have forgotten what it meant. Please pardon my conceit in thinking you have too.
GAMBOGE
Pronunciation: gam'bowj


Matching Terms: gamboge tree, Gambogian


WordNet Dictionary

Definition: [n] a strong yellow color
[n] a gum resin used as a yellow pigment and a purgative


Synonyms: lemon, lemon yellow, maize

See Also: gum resin, yellow, yellowness

Why not just say 'yellow moustache'? I don't think 'gamboge' adds anything here...other than showing that the writer possessed a smarty-butt (hi, Consuelo!) word.

O.Henry was very well read, and had a very large vocabulary.
Which like the rest of us, he enjoyed showing off.

With all due respect shown to Mr. Henry, I think in this instance the use of 'gamboge' covers more than it should--unless, of course, the narrator is trying to tell us more about this gamboge-moustached character than I know since I haven't read this story...least I don't think I have!

Well, the definition does say a strong yellow. Perhaps O. Henry thought gamboge was more precise than just yellow.

Bingley

But he was also showing off his scholarship to impress
his vocabulary challenged readership. And they loved it.