Hi Peter,
On the original post's first shot, repeated above, for me the Auto WB spoiled it, it looks far too magenta now, making the B&W the favorite for me.
Maybe the original was a touch too green, but the AWB version is about 3 or 4 times too far the other way.
To futher discussion of the topic witha couple of 'pet' theories
I think there may well be an atmospheric effect occuring here, if the landscape between camera and subject is highly saturated, the light falling on it is going to reflect back up and illuminate all the mist particles, giving them a cast. The effect is obviously going to vary depending on the nature of the mist and the thickness above to the skylight illuminating from above.
Further, without an optimal* lens hood, the extra light illuminating the lens elements is going to probably give increased veiling flare too and the colour and amount of that is going to depend on focal length (because certain element groups will be nearer the front at certain focal lengths.
* remember that it is designed for the 18mm end with that lens, so it must be sub-optimal at longer focal lengths.
Cheers,