This is a wonderful example of a Cape of Good Hope 1863-64 SG 21a, the 1 Shilling Pale Emerald Green. 

This one has full margins.  It is Mint Very Fine Condition with Original Gum.  As you can see from the photos it is a spectacular stamp, and the triangle design gives it a more unique and distinguished aesthetic.  It is valued at L1400 in the Stanley Gibbons Catalog.

This item is over $100 USD so I will ship it using priority mail in the US, and registered mail overseas.  This is is to ensure that it reaches you in a safe and timely manner, and includes tracking!