So, quick history of pigments outside of Venice: ultramarine blue was used primarily in painting the Virgin Mary’s robes until the early 17th century, when it kind of branched out into other forms, whilst carnelian and crimson reds had been associated with Christ’s robes and blood until a subtle shift in the Reformation and Counter-reformation created a need to use color differently. Only Venetians really used color differently during this time period, and it was mostly because the amount of fucks they had to give was a big fat zero. Venetians gave zero fucks. Venice was the home of no fucks given at all. This is partially why the sky in this painting isn’t a more vivid and realistic color of blue for the sky, and why Apollo’s robes are a duller shade of red, rather than the godly/kingly shade of crimson.