Many points already contain"Yin" or "Yang" as part of their name. These point combinations are used based on their inherent properties. For example,
Zhiyin (BL67) "Reaching Yin"--Zhiyang (DU9) "Reaching Yang"
Yinjiao (RN7) "Yin Intersection" --Yangjiao (GB35) " Yang Intersection"
Yinxi (HT6) 'Yin Cleft" --Yanggu (SIS) "Yang Valley"
Yingu (KI10) "Fin Valley"--Weiyang (BL39) "Lateral to the Crook"
Yinlingquan (SP9) "Ying Mound Spring" --Yanglingquan (GB34) "Yang Mound Spring"
Sanyinjiao (SP6) "Three Yin Intersection"--Sanyangluo (SJ8) "Three Yang Luo"
These combinations above are all derived from the origin of the points. In Chinese medicine, the concept of Yin and Yang can be extended to the following combinations : anterior and posterior, inner and outer, etc.