Official Github Brand Colors (August 20, 2015) from the GitHub internal CSS framework (Primer) version 2.3.3 at: http://primercss.io/colors/ [Note: Photoshop users. You can download the raw file (.css) and import the swatches just like a .aco file (more recent versions of Photoshop).

github-brand-colors-aug-2015.css

/* # OFFICIAL GITHUB BRAND COLORS
-------------------------------------------------------------------- 
Official Github Brand Colors (August 20, 2015) from the
GitHub internal CSS framework (Primer) version 2.3.3
Source URI: http://primercss.io/colors/							 

 1.a = Github Branding Color Swatches
-------------------------------------------------------------------- */
 .swatch-github-blue {
	background-color:#4078c0;
}
.swatch-github-green {
	background-color:#6cc644;
}
.swatch-github-red {
	background-color:#bd2c00;
}
.swatch-github-orange {
	background-color:#c9510c;
}
.swatch-github-purple {
	background-color:#6e5494;
}
/* 1.b = Github Branding Grayscale Swatches
-------------------------------------------------------------------- */
 .swatch-github-gray-light {
	background-color:#999;
}
.swatch-github-gray {
	background-color:#767676;
}
.swatch-github-gray-dark {
	background-color:#333;
}