use of colornames & validation

On the next w3schools page I got the following information about the use of color-names
http://www.w3schools.com/html/html_colornames.asp 
  
QUOTE:
Note: If you want your pages to validate with an HTML or a CSS validator, W3C has listed 16 color names that you can use: 
aqua, black, blue, fuchsia, gray, green, lime, maroon, navy, olive, purple, red, silver, teal, white, and yellow. 
If you want to use other colors, you must specify their RGB or HEX value. 
END OF QUOTE

So, how come that when a colorname that is NOT in the 16-list is used, the w3c html-validator still validates the page, 
instead of coming up with an error ??

Just curious
sherill