Could someone explain to me what purpose this code serves? I found it in the source code in the <head> of the page for this site http://blog.brianbeck.com/tagged/jquery
<!-- Default colours -->
<meta name="color:Top Border" content="#333" />
<meta name="color:Site Title" content="#D53C2E" />
<meta name="color:Link" content="#333" />
<meta name="color:Link Hover" content="#D53C2E" />
<meta name="color:Button" content="#ccc" />
<meta name="color:Button Hover" content="#D53C2E" />
<meta name="color:Post Title" content="#333" />
<meta name="color:Post Title Link" content="#D53C2E" />
<!-- Default social link text -->
<meta name="text:Website Address" content="" />
<meta name="text:Blog Address" content="" />
<meta name="text:Flickr Username" content="" />
<meta name="text:Twitter Username" content="" />
<meta name="text:Facebook Username" content="" />
<meta name="text:YouTube Username" content="" />
<meta name="text:Lastfm Username" content="" />
<meta name="text:Delicious Username" content="" />
<meta name="text:FriendFeed Username" content="" />
It is something unique to tumblr
“Enabling Custom Colors
By including the special meta-color tags in your theme, users you share your theme with will be able to easily tweak those colors using their “Customize Theme” screen. ”
The meta tags are essentially used as variables which users can change. They are referenced by the Javascript code on the page to make them automagically work.