First case of color dimorphism in pholcid spiders
Published in Journal of Arachnology, 2004;; PDF

This study presents the first case of a color polymorphism in the spider family Pholcidae, based on large series (1139 specimens) of the east African Buitinga safura. About 6% of specimens have large black spots on the abdomen, all others are spotless.

For a more recent review of color polymorphism in pholcids (mostly intersexual but also intrasexual) see here.