I've been creating stored procedures using Oracle SQL developer.
For some reason, one of the icons does not contain a green circle. What gives? What does this non-green icon mean?
I believe the green circle you're referring to is actually a green bug icon. That indicates that the procedure has been compiled for debug.
If you are editing a stored procedure in SQL Developer, there should be a gear icon at the top of the edit screen that you use to compile the procedure. If you click the arrow to expand that, you should get options to compile the procedure or to compile for debug. If you select "Compile for Debug", you'll get the green bug icon. If you select "Compile", the bug icon will go away.