Hi Kat - the Zoo has two white-cheeked gibbons located in the World of Adaptations building. The male is black with white cheeks and the female is white with black around her eyes and mouth. However, it seems like you may be describing our white-faced saki monkeys. The male is black with a brightly colored orange mask, while the two females are brownish-grey in color. To clearly identify the species, please feel free to visit our animals on exhibit at www.rwpzoo.org/animals.
White-cheeked gibbon Nomascus leucogenys I believe these are the ones you saw
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