This was sufficiently below the 256 maximum that everyone could have their system colors. You could give each dot a total of six settings, and define 216 colors that. Being engineers, they just took the 256 settings available for each dot in an 8-bit system, and divided by six. So, the system of Web-safe colors allowed for any color to be described by using one of these six numbers for each of the three primary colors. They thought it would be more interesting to use a completely different numbering scheme called hexadecimal, which instead of having ten numerals has 16.
Computer engineers love to do stuff like that, which is why they are so much fun at parties.
1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,10,11,12,13,14,15,16,17,18,19,1A, 1B,1C,1D,1E,1F,20,21, etc. These are the same numbers, just expressed in a different numbering system. Why this matters You might wonder what would happen if you used a color that is not one of the Web safe colors. It is the people that are only displaying 256 colors that you have to worry about. If you use a color that is not Web-safe, such as for a background color for your page, the result could turn out like this.