-
Gray Hat SEO is between the white hat and black hat SEO. Gray hat SEO is SEO techniques that take more risks than white hat SEO techniques but aren't likely to get your site banned from search engines (although a search engine penality could result).
-
Gray Hat SEO is an SEO practice that's riskier than White Hat SEO, but one that may or may not result in your site being banned from search engines and their affiliate sites.
-
Grey Hat SEO is mixture of White and Black Hat SEO techniques.
-
I have no idea about blue hat SEO. Gray hat SEO services tend to use some equipment and some questionable to assume greater risk.Gray hat SEO techniques are not well defined in google's search engine optimization guide.