Hey Mark.
I don't really know what you mean by "neutralization of White Hat and Black Hat", but as far as I know, Grey (or Gray) hat SEO is all about questionable SEO techniques that lie somewhere between White and Black.
They are riskier than White hat SEO techniques, but aren't likely to get your site banned like the Black ones. A penalty could result though.

Such a technique is for example using a quite high keyword density (not stuffing though, that's already Black).
Or planned three-way linking, or a few paid links to increase link-popularity instead of only traffic (not using the "nofollow" attribute as you should) and so on.

Don't forget though that grey is a shade of black, not white, therefore grey can easily become black when overdone.
When it raises a red flag and is detected by search engines, Gray hat becomes Black instantly.

And one more thing: even if the search engines can not detect the tactics you've used, your competitors could still report your site to eliminate you from the competition...