What is this yellow section around the cockpit window?
You're right. The aft no. 3 fixed window has a reusable retainer with 2 rows of fasteners- one for holding the window glass and another for attaching to the fuselage, as can be seen in this PPG document- this is the two rows of fasteners in the image.



A320 aft window, image from Cockpit Windows Technical Data from PPG Aerospace

My guess is that there was some damage to the area and the airline replaced the whole assembly and sent the aircraft before the primer could be painted over. When painted, it would look some thing like this:



A320 window, image from miles-around.de

Note: The A320 does have an emergency (sliding) window in the cockpit- however, it is in the no.2 window, the details of which can be seen in this document