When I shoot Portra 4ooUC, I do so exclusively for outdoor portraiture in the Autumn only. It enrichens Autumns deep reds, oranges, yellows and browns, ultimately warming the human subjects among the colour.
I have heard that film producers customize film for different markets. i.e. the same Kodak Portra 400UC film for sale in the US will be different than the same film for sale in Europe, due to differences in light strength. Is this true?