Painting Clouds can be challenging but fun. Best idea is to study them for awhile and sketch them to get their values, shapes and edges down in your mind.
I used a palette of Cad.yel, cad. orange, cad red., aliz.crim, ult.blue, cerulean, dioxazine purple with white, viridian and titanium white.
Mix ultramarine blue and white for the top plane and work your way down gradually getting lighter and adding a newer mix of cerulean blue and white toward the horizon.
Using titanium white with little cad.orange, paint in the clouds. Mix a shadow color using cad.orange and little dioxazene purple. Using flat brush paint in the shadows. Allow some edges to stay sharp.
Soften some of the edges along the top with a dry round brush and bit of medium.