Have you ever taken a painting class online? I've taken quite a few art marketing and business classes that way, but The Painted Sky from Deborah Paris' Landscape Atelier is the first class I've taken online where we actually paint. It's hard work, but well worth it.
These are some of my studies from the first lesson, which was on gradations in the cloudless sky. Note that some of them are graded top to bottom and some include a side to side gradation related to the location of the sun. The top painting is from my own observations just before sunrise in Seal Bay on Vinalhaven. Deborah suggested a little more blending on that one. The others are from paintings by Maynard Dixon, where I copied only the sky. You'd be surprised how gray these skies are compared to out-of-the-tube paints mixed with white (my pre-class approach).