Blue sky isn’t the same color blue everywhere, especially if your modeling the Los Angeles area. I used a photograph of the San Fernando Valley taken on a not so smoggy day, then matched the blue sky in my photograph to a True-Value Hardware paint sample card. You’ll notice in the real world that sky get lighter towards the horizon, almost to white. I bought quart can of each color needed, Light Blue and for the white, I used a True Value color called Silver Sand.
I set a piece of Masonite on the wall brackets that works as a table for holding my paints and brushes, also keeps drips off the floor. I prepped the wall by filling all those picture hanging nail holes with filler and smoothed with fine sandpaper and used blue painters tape to edge my masterpiece. I started with the Light Blue for the first coat, it looked a bit dark at first, but a second coat of Light Blue and also mixing with Silver Sand lightened up towards the horizon made the sky look better. I use a 1 1/2″ wide brush to do my painting. Don’t rush, keep the wall wet with paint as your adding the Silver Sand color, work only several feet at a time. Watch for runs, so keep a rag handy.
While working the Silver Sand with the 1 1/2″ brush, I painted the softer looking clouds midway in the backdrop (these are the easiest clouds to paint), and continuing into a haze to the horizon.