I am new to CB and am having problems trying find the registration page. Is it a module? Is it a plugin? I would like to modify that page if possible. The form on the page shows white font for the gender question so you can not see it.

The registration form is generated from your tabs and fields within CB > Tab Management and CB > Field Management. It is not a static HTML page that you can modify. Your font color issue is a problem coming from your Joomla template. You should be able to fix that with some CSS. Right click and inspect element on the radio inputs then review their label CSS in the developer window.

Also on the profile page there is a large grey box over top of the profile picture. Can you please tell me where that is to modify.

That's the canvas. Their profile background image. Users can upload a new image. If you don't like the default gray you can change it by editing the canvas field withing CB > Field Management and adjusting its parameters accordingly.