This was an error, printing with the colour for the 2s Blue. Footnoted in Campbell Paterson.
Authorised for postal use since at the time of issue there were no available postage stamps in this denomination. Comment in SG catalog on the watermark: In its sideways format the watermark exists indiscriminately sideways (left or right), sideways inverted, sideways reversed and sideways inverted plus reversed. Individual listings are not given for these variations.
The watermark image shows possible orientations.
