It was just being mocked up in the first pic. It hadn't been stripped of the origonal paint yet. The header panel didn't need to be sprayed with poliester primer so it was masked off.
The factory painted everything together except for the front valence and side louvers. The front valence was installed after the blackout process was done and the louvers after the stripes went on. You can do it any way you want. If you paint it all together, you don't have to worry about retouching any of the bolt heads later on.
I've never liked the look of the 72-74 cars when the front ends were painted anything other than body color. The same goes for painting the hood scoops black. The factory painted them body color and that's how they look the best.
Blue with white stripes is a great looking combo.