Hopefully I don't need to tell you which is which. Velvia 50 above, with the typical Transparency film bluer than blue sky. below, just a little too much cyan for me in the Portra 160 sky. But that is also typical of C-41 films.
Here the same view, taken minutes apart as I had just changed film............This sun angle make the Portra sky more tolerable for me.......But I still prefer the true blue.