What color/treatment would I put on the underside of the front fenders? Body color? Undercoat? Primer?
On the front center hood scoop, behind the opening, Is that area painted black or is it body color?
The underside of the fenders only has overspray of body color. There is no need to undercoat fiberglass
Inside the scoops is painted black
The entire nose was assembled as bare raw fiberglass with gray sealer on exterior surfaces then exterior was painted body color. On backside you would see mixture of combination of white, gray and pink fiberglass with black sealer and body color overspray. There also is frequently a banding of what I would call aqua around radius of inner wheel lip.
To add- there is a bonding strip that adheres the lower front of the fender to the main fender body. On ether side of the bonding strip is a dark gray epoxy that squeezed out during the attaching process. The contrast color of the epoxy can be seen through the typical overspray in that area.
Some pictures I hope will illustrate
In this one the gray epoxy is there but the front support bracket isn't any longer
(https://www.concoursmustang.com/forum/gallery/18/6-250623165636-187802218.jpeg)
Same thing here
(https://www.concoursmustang.com/forum/gallery/18/6-250623165643-18784878.jpeg)
A little off focus of the the thread but a look at this example from above the headlight area
(https://www.concoursmustang.com/forum/gallery/18/6-250623165642-18783535.jpeg)
(https://www.concoursmustang.com/forum/gallery/18/6-250623165641-187822406.jpeg)
(https://www.concoursmustang.com/forum/gallery/18/6-250623165636-18780950.jpeg)
Jeff posted a very typical look from under the fender. If you understand how the front clip was done off of the car you can see how the overspray patterns formed.