Russia 1931 #C23a MNH OG 50k Russian Zeppelin Airship Airmail Error EX-F Mi400 B

Russia USSR 1931 #C23a MNH OG 50k Russian Zeppelin Airship Airmail Issue, Error in color, Extremely Fine Superb condition. Mi 400 Bxb.  Perfect centering with thick margins.  This is a rare stamp with only 3000 printed- rare to find one in this nice condition.  I am collector (non-dealer) and this will be a great stamp for any foreign/ Russia collector. 

Shipped USPS priority, tracked, insured.  

Thanks for looking.