Buffy sakis are characterized by their long, coarse, fluffy hair. Their hair is mainly white or cream colored, with brownish black colored hair extending from their elbows to their wrists. Their tail is entirely black. Small patches of brown or black hair are also noticeable on their hind limbs, and from the nape of the neck to tail. Their hands and feet, however, remain white or cream colored. The hair on their tail and trunk are longer than those on the forearms and hind limbs. Their underbellies are very lightly covered in hair. The hairs on the crown of their head are directed forward like a hood and sometimes overlap the facial region, making it look like they have bangs.

Male and female buffy sakis are sexually dimorphic in color—also known as sexual dichromatism. Males’ facial skin is mostly black with small pinkish skin patches above their eyes and distinct white-to-cream eyebrows and cream upper lip hairs. Females’ facial skin is also black with cream-to-white eyebrows, but with white or cream-colored malar stripes (from the base of their mouth to the side of their neck) that extend out to the cheeks. Older females have more white covering their face than juveniles or subadults.

Adult males and females also have large scent gland patches on their throat, which are ringed with a light orange color. The orange ruff is more prominent in males.

When approached in the wild, the hair easily piloerects or “puffs up” as a threat. This tends to make them look bigger than they actually are. The length of the tails of buffy sakis are equal to their body length. Their tails are not prehensile, but the hair on the tail does “puff up” when approached or if they feel threatened.