2.1.3 [CSS3Color:2011] Section 4.2.1, RGB color values

V0005:

The specification states:

 The format of an RGB value in the functional notation is ‘rgb(’ followed by a 
 comma-separated list of three numerical values (either three integer values or 
 three percentage values) followed by ‘)’. The integer value 255 corresponds to 
 100%, and to F or FF in the hexadecimal notation: 
 rgb(255,255,255) = rgb(100%,100%,100%) = #FFF. 
 White space characters are allowed around the numerical values.

Quirks Mode and IE7 Mode (All Versions)

Signed RGB values are not supported.

IE8 Mode (Internet Explorer 8)

Signed RGB values are not supported.