I am probably showing my age but in the old cowboy films the good guys wore white hats and the baddies had black ones.
It is no surprise then that the Search Engine Optimisation (SEO) industry refers to those who recommend dodgy tactics to their client as "Black Hat SEO's".
Just when I thought I had seen it all I met with a pucker accountancy this week who had an entire section of hidden text on their home page. The concept isn't hard to grasp. If you have a purple background on your website then you put purple text on it. Humans can't see it or read it but search engines can. The whole thing is designed to trick or manipulate search engine results.
Google take a pretty dim view of this and other black hat tactics.
Google do offer some help and advice to webmasters. This is what they say about hidden text:
If your site is perceived to contain hidden text and links that are deceptive in intent, your site may be removed from the Google index, and will not appear in search results pages.
The accountancy firm risk having their website banned from search engine results as a result of the advice they were given.
Sometimes this type of advice comes from web designers who don't grasp the concept of legitimate SEO tactics too well. Sometimes it comes from Black Hat SEO companies.