Great Britain 1973 3p Harrison Colour Trial, SGX844.
A very fine unmounted mint, with full original gum, imperforate colour trial printed in olive-grey, produced as a proof for the "Jumelle Press" trials in specially prepared sheetlets of four, this being the bottom left corner example.
Printed in the issued 3½p colour (SGX858).
A scarce Machin colour trial.
