This word is now so rare that people who write about it usually quote from one of its last unforced appearances, Lew Wallace’s Ben-Hur of as long ago as 1880 (“each compartment crowded with labelled folios all filemot with age and use”). Here’s another, from a little earlier still:
October now. All the world swings at the top of its beauty; and those hills where we shall live, what robes of color fold them! Tawny filemot gilding the valleys, each seam and rut a scroll or arabesque, and all the year pouring out her heart’s blood to flush the maples, the great impurpled granites warm with the sunshine they have drunk all summer!
The Atlantic Monthly, Feb. 1860. We may perhaps forgive the writer’s strained and impassioned, even impurpled, prose, since she goes on to say that she is to be married at noon.
You may by now have guessed that filemot (said, if you please, as three syllables, and not as file-mot) is a colour, the russet or brown colour of dead autumn leaves.
It began as the French feuillemorte, literally “dead leaf”. It has occasionally appeared in that spelling in English, either as one word or two. However, the extraordinary ability of my English forebears to transmogrify any word coming from across the Channel has changed it into phyliamort, philimot, foliomort, fillemot and other forms.
You may instead, if you prefer good plain words, resort to pure-bred English and refer to it as dead-leaf brown.