Something people get confused about with colour is how, by simply being very selective with the frame, you can end up with surprising colour contrast in the same lighting conditions - even with Portra.
But more importantly, you have to ask yourself whether the 'style' that you're seeing is actually the photographer's shooting aesthetic (his response to tonality, colour and lighting) or, whether there is something unique in the processing - magic bullet. In my eyes, there isn't, and what you're seeing is his own subjective and idiosyncratically personal sense of neutrality. It's very hard to imitate the way somebody else's brain processes colour! Straight photographers like this rely very much on intuition.
The way we respond to colour at the actual shooting stage (surprising how many colour photographers don't actually see in colour) is about taste and aesthetic sensibility, but also intention with colour relationships (look up 'colour theory'). What strikes me about these pictures is the photographer's very subtle eye for colour - i.e. what is inherent in the scene. They are otherwise very, very straight and unaffected pictures. Very good too.
The most important thing with colour is going out and developing a responsiveness and sensitivity to it, otherwise, due to its rabbit hole complexity, it can very easily become science. At which point you'll find that photography is very superficial.