Many artists and painters paint tonally. That is they paint the colours of the shapes - either as they believe them to be or as they observe them. (There is a often large difference here). The overcast provides plenty of tonal opportunities. Most people prefer to paint in full sun. However, to learn to really see what is happening in full sun, overcast provides fertile training.
Here is a painting done at roadside in LaCloche ducking the showers but aware that the sun actually was teasing us with a few warm spots in the sky.