Sky replacements are a common request for a colorist to perform and there is a real advantage to being able to do them in the grade, rather than leaving them to VFX.
Mad Max:Fury Road colorist Eric Whipp commented in an interview with Filmlight, makers of colour grading software Baselight, that he and the team performed hundreds of sky replacements for the film, evening out differences in the production footage and to enhance the iconic look of the film.
I’m not sure of the total count, but we must have done hundreds of sky replacements in Baselight. To get the rich look, we often found that some kind of blue sky helped make the image more graphic, particularly when a cloudy shot is cut next to a sunny, blue sky shot.
Using the tracking in Baselight, I was able to add skies to so many shots with relative ease. The main reason for doing these in the grade instead of VFX is that the sky could be changed at any time and adjusted with the grade as the look was developed. This development began very early on in the post-production process.
— Eric Whipp, Colorist