You can change the little, yellow email graphic that Radio uses by default in your template. I found an email graphic on google images that I want to use. It looks like this.

In the Radio application, Choose Tools, Developers, Jump...
Enter 'radio.macros.mailto' without the quotes and hit enter.

Look for the following image code.

Change the code to match the new image that you'd prefer. For this example, I've changed it to the following:

Hit the Compile button and then close the window. Repost any pages that you want to have the new image.