First of all, the various social media network logos are indeed all TRADEMARKED. Twitter and Facebook, for example, have lengthy pages about how to format their logos. They make it sound like it is absolutely illegal to modify these icons for use on your website.
These rules are simply suggested guidelines. We've all seen social media icons in every format and color. The Hello World Design website uses a monochrome color palatte, and to keep a uniform look to the site, all of our social media icons in the footer have been modified. Twitter may not suggest I put their little bird icon inside a circle.. but I see no need to have a blareing blue icon being the focus point of our website.
This is something a lot of website designers out there may be asking. Hope this helps!