Generally considered to be European rather than English or Scottish, after the First World War it started to appear in England in arms and badges relating to the Royal Air Force, though it is still doubtful if any more than a dozen examples could be found in British heraldry, and most British heralds consider it unheraldic. While in the post-World War I period bleu-celeste is depicted as a darker shade, in prior times it was depicted as very light, and has even been treated as a metal, as azure charges have been placed on a bleu celeste field, and vice versa.