Purple skies are the result of the phenomenon called "scattering". Scattering of light by molecules of oxygen and nitrogen in the atmosphere makes the sky blue. But the magical purple colour can form when the air is supersaturated with moisture and storm clouds hang low in the sky.
It is probably unlikely you will actually find a purple sky or clouds! I was lucky in that my sky was a beautiful mauve. However, with magic of Lightroom I was able to add a purple filter and ta da....purple skies for you and me!
Find some clouds and see what kind of purple magic you can add. Or, find something purple to highlight in the clouds such as a kite, scarf, flag or flower!