A colour name popular in the textile and allied trades since 1550. Standardised in 1934.
Really an improper name for a specific colour sensation, since Saxon Blue, from which Saxe is derived, is the name of a chemical substance only, a dye from which are produced all tones of blue from light to dark.
The word Saxe is not English but is adopted from the French, where it means Saxony or Saxon.
Saxony Blue was a universally-used synonym for Smalt as early as 1550.
Likewise Bleu de Saxe has long been a synonym for Prussian Blue, but since 1753 Saxon Blue has been most familiar as a widely-used name for indigo extract.