Syria Alaouites 1926 Airmail Overprint Colour Trial? Set Mint SG44-47 footnote?

Alaouites airmail overprint colour trial? set of 4 mint. With the airplane in red - am not sure what Gibbons means in the footnote as the airplane is red in the original stamps. Mounted mint with hinge remnants.

Year : 1926

Reign : Not Applicable

Catalogue No : SG 44 - SG 47

Condition : Mounted Mint

Price : £5.00