Great Britian 1912 Stamp King George V

Pigments for the inks used for printing stamps were, primarily, sourced in Germany (if I remember correctly IG Farben). Because of the war, the printers experimented with different pigments. This is one reason there are many "shades" for the MacKennal stamps with Simple Cypher watermarks. Many can be attributed to wartime printings. However, "shades" also are known from earlier and later printings. The Block Cypher issues of the MacKennals printed long after the war, also, have plenty shades.

Since the stamps posted by Stamps4Life are Downey Heads that were discontinued before the war, this is highly irrelevant for those. As for the stamps posted earlier, evidently, not all are wartime stamps.

Edit: note OP's stamp was cancelled in 1920, so the chance it is a wartime printing is not very big.

Seems IG Farben was formed from a merger of BASF and others in 1925. Pre-war (according to Wikipedia), the main suppliers of dyes would have been BASF, Bayer and Hoescht, with five smaller firms producing speciality dyes.

British Dyes Ltd. was formed in 1915 to supply dyes to the textile industry. This merged in 1919 with Levinstein Ltd. to form British Dyestuffs. Ivan Levinstein was a major force in developing the British dye and pigment industry. He developed Rosaline magenta and red azo dyes.

IG Farben was IG since 1916. All constituents produced colours and were co-operating from 1904. IG Farben AG was the official merger of the companies making up the IG.