Winter or snow teas (雪茶) are as the name suggests, seasonal, and also rare due to the fact that most teas are harvested in either spring or autumn, tea picking usually end by late autumn. How is the winter variety different?
Oolong teas are semi-oxidised teas, they are neither green nor black but a category of its own. Oxidation is a process that exposes tea leaves to air which in turn contributes to its dark colour and aroma. Similar to how an apple turns brown when its left out in the air for a period of time. Green teas are barely oxidised while black teas are fully so. Lighter Oolongs are oxidised for a shorter period, while darker Oolong teas are oxidised longer.