Everyone seems to be using incorrect version of the branding for Twitter and Facebook graphics. They both have easily discovered pages on their respective sites illustrating how their logos should be used.
Your icon linking to your Twitter page should be just the bird, not a ‘t’.
“While you may scale the size to suit your needs, you may not modify the “f” logo in any other way (such as by changing the design or color). If you are unable to use the correct color due to technical limitations, you may revert to black and white.”