The colors were natural as they were, shot @ 1/500 which only my cam(along with D70s and its other predecessor) can achieve. and Irisviel is a happy person if you have seen the whole series Just like the scene where she was driving a car with Saber.
I've read all the Fate/Zero novels, watched both seasons of the anime and the specials, and even cosplayed as Irisviel. It's just that the coser's expression comes off as scary instead of the regular happy or demure kind of expression Iri has.
Because the contact she used are a solid red where the limbal ring and pupil aren't very obvious, her eyes look like one solid red circle from far (since I can't zoom in much for this photo). It's kinda hard to see any expression in the eyes due to the face that the red seems to be a bit overpowering. To me it just comes off as a glare.
I'm guessing it's the angle, since this shot from a different angle captures Iri's expression better: [link]