Image No 1, I think that's part of your problem here Andy, that you haven't over exposed them enough, with snow shots you normally have to overexpose the image, left to its own devices the camera will try to evaluate and average all the tones and it generally comes up with middle grey or there abouts, the snow fools the camera's metering.
I normally a focus on a well lit area of snow and dial in about +1 EV of compensation, after dialing in the compensation I take a meter reading on the light area then flick to manual and dial in that aperture and shutter speed so nothing changes. Then take a shot, the histogram should be ramped up to the right as far as! I found that deleting images in the camera cos they look over is a mistake! Until you look at them on the screen, you can't really tell. Also sometimes I have found using flash WB works because snow has a bit of blue cast.
I hope I'm not telling you how to suck eggs! If so tell me to do one!
I also think that as mentioned above the colour of the sun might have something to do with it, but generally the brighter the day the day or ambient light is the more compensation you have to add.
Anyhow I love image No1, love the silhouette of the tree against the sun, I don't think the white is too off. (Look in the well lit areas to the right) I think the shadow cast by the tree is giving you the grey cast as its under exposure of the snow in that area. I love those great segmented slabs of snow, and the sun brushing across the snow tablets.
Hope this makes sense and you probably know all this anyhow so.....
Cheers
Steve