Painting the sky is always great, sometimes a challenge if the clouds are moving quickly, but just as the sea can have every colour you can think of in it, so can the sky, though I recommend always having Cerulean Blue available as any sunny day with clouds will have the almost pure colour out the tube in it!
That and in England there’s that grey blue/purple on the base of the cloud and bright yellow/white edges of the cloud with every combination in-between!
Worked on the Belfast Ferry picture today, which I’ll now ‘park’ till another day and concentrate tomorrow on the 12 London picture work and on Friday paint outside on the edge of the Mersey.