You will not be able to pass the image to the next page this way. When you have an input in a form it is the value that will be posted. You will need some way to associate the image with the selection. Do your images all relate to the choice directly? In your example the value of the radio option was Black, and the image was Black.jpg. You could use the value of the radio selection to show the image on the next page with some code like this:
<img src="../Colors/formimages/<?php echo $_POST['BallColor'] ?>.jpg"/>
This is using the posted reference for the variable, you would want to use your session variable that is holding this value in it's place. If all of your options and image names match up like this then this would be one way you can get the image for the selection made to show on the next page.