Had a storm today and tried to match the colour of the cloud. Ultramarine with a bit of black seemed to do it. I’m not sure if the paint in my box that looks like black really is black. It could be indigo.
I notice the new versions of my paint set have white instead of black/indigo. I wondered what use whiote would be when you could just let the white of the paper show through a thin wash. So I tried mixing with white in the second set of swatches. Still no idea – small highlights?