We had a number of pics. sent to Storm Team 8 of a purple sky Monday evening in SE Kent County.
First, light from the surface of the Earth can bounce off low clouds and we can see that light here on the ground. Check out the picture below of the Kīlauea Volcano in Hawaii illuminating the (smoke) clouds above it:
I can’t at the moment say for sure (I’m on vacation this week and am on the NW side of the city), but I’m pretty sure this is a reflection from lights in a greenhouse. Check out all this pics. on Google Images.
The pic. above is purple greenhouse lights at a greenhouse at the Univ. of Cal. at Santa Barbara. These purple LED grow lights are becoming more popular. They are more energy-efficient and plants like the full-spectrum red/blue color.