This is Scott #973 Issued in 1982.
Unitrade mentions varieties of this stamp with Orange background, but I don't really think that is it?

Unitrade: "Repellex error, part of colour missing on part of one column of 10stamps. Four sheets are also known with similar error causing 40% to 60% of the background of all right margin stamps to be orange rather than bright red.

Definitely not 40% of the background. But I do note that the orange never seems to extend into the white.