My first time using a HDRi image for the lighting source. I then realised the brilliant potential of HDRi! It's a superb thing to me. Well, try creating realistic lighting without it. I think I entirely chose the wrong HDRi initially - but when I chose a more appropriate one all of a sudden the car became the correct white.

Realistic shadows are imperative and I added a Mapping node in Blender to swing the HDRi around and have it cast a shadow directly beneath the car - like the otehr vehicles in the car park.