I had the pleasure to visit Croatia and the sky seemed familiar to me somehow... and I realized I was on the opposite coast of the Adriatic Sea. What I remembered was how it was rendered in Porco Rosso, which I had seen years before visiting IRL.

Watching the movie again, I am amazed at how precisely Miyazaki captures the exact feeling of the sky and sea of the Adriatic in summer.

IIRC Porco Rosso is supposed to take place at least partially in the Free State of Fiume (https://en.wikipedia.org/wiki/Free_State_of_Fiume) that while eventually annexed by Italy in 1924, after WW2 it became Rijeka, now the third largest city in Croatia (https://en.wikipedia.org/wiki/Rijeka).