One of the largest ethnic minorities in Vietnam is the Hmong Tribe. Hmong originally means "free people". They came from China, and now live in different regions throughout Vietnam. The Hmong minority is divided in several subgroups. It is very easy to identify them, looking at the color of the clothes they wear. In the picture you can see a mother with her child. She belongs to the Black Hmong tribe.
By the way, when you come to Sapa, bring an empty bag. I am sure you won't resist the temptation to buy some of the handmade souvenirs on sale in the shops. You will find silver bracelets, clothes, pillows, blankets, hand bags... at an exceptional price. You will also find Sapa souvenirs in every major town in Vietnam. When buying souvenirs made of fabrics look for imperfections. These are the ones made by local people. The souvenirs "too" perfect are produced in industries somewhere else (China).
Vietnam Travel - Sapa Travel Guide