Color, generally, is ascribed with ser. In the mental model I'm assembling as I learn Spanish, this seems to be because it is, generally, a durable characteristic. El cielo es azul - the sky is blue.
What is the correct verb for a temporary color that reflects a state? For example, 'the sky is grey'. Is it el cielo es gris, because it's a color, or el cielo está gris, because the color is being used to describe a present state? Or is that kind of construction not used?