Hylobates concolor are between 18 and 25 inches heigh and weigh approximately 12 to 20 pounds. When H.concolor is born, the coat is a buff or golden color. After it reaches about six months old, it turns black. Males remain black and have whitish fur around their cheeks and on the top of their head.
Females turn back golden or buff when sexual maturity is reached, sometimes with black patches.
The body is small with an erect posture. Their long arms and legs assist in brachiation. Hook shaped hands assist in locomotion as well. The thumb extends toward the wrist. This allows a better range of motion for traveling and feeding.