Switzerland: Airmail labels 5

Here is a very rare airmail label from Switzerland.

Year: 10.5.1925, Gummed. Günter Mair's catalogue no: - SWI-C-19, perforated 11 ¼ , sheets , Intended for special airmail, Basel, 10.5.1925, black-blue/white, but my one looks like dark brow. 
5*****