Gases and particles in the atmosphere scatter light, and since blue travels on shorter, smaller waves, it causes charged particles to move faster, scattering more light. So we see more blue than we do red because blue gets particles worked up more than the other colors. Our eyes are also a bit more sensitive to blue light, which helps. Violet is always there, but we don’t detect it as well as we do blue, so blue wins the light wave battle for our eyes. The right conditions have to be met for purple, or violet, to be visible. This was during that right condition , the sky turned it’s colour and shot right. I included this security stand against the backdrop which gave it a separate perspective.