Term- "Web Safe Colors"?

Question: Term- "Web Safe Colors"!?

How Many Web Safe colours are available for designing web Content!?
In Photoshop, Option called "Only web colors" contains only 4 Shades of gray!.!.!.
Please guide,
Do it is necessary to use that colors Only!?Www@QuestionHome@Com

Best Answer - Chosen by Asker:

The web safe palette consists of 216 colors!. The only reason to use the browser-safe palette is if you have a concern that your Web design work will be viewed from a 256 color (8-bit) computer system!.

Most computers these days can handle thousands of colors and can display far more than the 216 web-safe colors!.Www@QuestionHome@Com