I really like the white background and the black edged outline. It shows the structure of the flakes better than anything else. Over the last few days, I have found a lot of so called "experts" on snow flake photography, and they mostly looked very amateurish to me, with images that were just terrible. Yours look like some of the best, so your definitely on the right track.
I have been noodling over an idea of using either some black PVC tube or maybe aluminum, if I can find it, to build sort of a Super Extender. All it needs is mounting rings on either end, then adjust the length to get a usable magnification. I think, using two Kenko tubes, mated with black tubing that is just big enough for the Kenkos to slip inside enough to tape them, would give you the mounts on either end. The rest would be a matter of manually focusing the lens on the end.