White. Black. Gray. What color of SEO hat should you wear to set foot on the safe part of the realm? Are you familiar with these hats? Maybe not.

Mark Jackson of Search Engine Watch has distinguished one from the other...

White Hat SEOs
These are the guys that abide by the guidelines set out by the major search engines. If your brand reputation and domain are highly critical to your company, this is probably the route you want to go. These folks are going to be using basic methods that have a proven history of success. White hat methods take time to ramp up and - in my experience - have tremendous "sticking" potential; that is to say, rankings achieved will be there for a longer period of time.

Black Hat SEOs
Some of the best SEOs in the industry are black hat students, if not practitioners. That is to say they are very technically minded and can do some pretty creative things to achieve rankings and try to avoid the "Google police" These folks may practice cloaking . ETA redirects, etc.

Gray Hat SEOs
Gray Hats are often, but not always, black hat wannabes. They may stuff some keywords into the alt text. They will probably have a link at the bottom of every page of a site that has "keyword A" linking to the home page. They may create a bunch of "information pages" that are strictly built to try to rank for a particular keyword but have little use to the end user/visitor of the Web site. Another method that some would consider "gray" are the buying of text links on various Web sites. Some competitive situations may make a white hat go a little gray on occasion, but most of the things gray hats get involved in are what white hats would consider ethically questionable, such as keyword stuffing, etc.