Colombian airmail stamps were overprinted in 1923 to be sold and used in various countries to prepay airmail service to Colombia. This example of the fifty cent green was bid up to $500, thereby exceeding catalogue value once the premium was added.
SCADTA #6 1923 50c green CA. overprint, fresh, mint never hinged single with selvedge at top, very fine. Unitrade CV$500, realized $575 including premium.