Paint is ALWAYS fading from UV light exposure. It IS slow and typically not noticed, but it happens. AND the amount/intensity of the light can vary from side to side AND color of the paint.
In the 1968 era, GM had a color that I termed "pale pea green metallic". After about one year in the Texas sun, the vertical parts of the car (hood, top, deck lid) had all faded to a more silver color, uniformly. The vertical sides were still pretty accurate to the original color. Light colors usually fade quicker than darker colors.
By comparison, the gold Chrysler had on their B-bodies seemed to fare much better, as to decreased fade and vibrance of the metallic, 40 years later.
To find paint that is the most true to the original color, that would be on the inside of the deck lid, I suspect. BUT if you are going to spot-paint, then what we used to term "hand matches" of the affected areas is the only way to go, with the mixer also doing "fine-tuning corrections" as needed.
When I was reading the Body section of my '66 Chrysler FSM, it mentioned how to shoot sealer in the drip rail pinch weld area. It ALSO mentioned paining and spot repairs. INCLUDING the mention of how gun air pressure can affect the final color, as to how the metallic lays out because of that pressure! The color might look exact in the "dab test" the mixers might do oni hand matches, BUT if the painter shoots it with a different-then-OEM air pressure at the gun, it can come out looking lighter or darker than it should, due to how the metallic flakes lay out as they hit the surface.
ONE other observation about "patches". EVEN if the new paint matches exactly to the original paint, the NEW paint will then age from UV exposure. The existing paint will continue its change in color from UV exposure, too. IN theory, they would both change at the same rate, but I have observed (on cars which were patch-painted) that all can be good for about three years before the aging issue will be noticeable, in both color value and surface shine. Metallic reds happen quicker than light yellows, too.
ALL cars were painted in what is now termed "single stage" acrylic enamel (Chrysler and Ford) and acrylic lacquer (GM). This is NOT the base coat for the newer basecoat/clearcoat system. The addition of the clear top coats will shift the base color from what it was without the additional clear on top.
In about 1984, after GM pickups had transitioned into BC/CC paint, we got a group of them in with a new metallic blue that reminded me of the earlier Chrysler B5 blue. We had to repaint many areas as the paint was soft, as delivered to us. I commented to our painter that it looked like it was a Chrysler color, but a few shades off. He later said the paint people had confirmed my suspicion. The base coat was the same as that earlier B5 blue, but the clear coat on top shifted it enough it was a few shades different.
Ford had a little different approach with their "glamour colors" for middle 1970s Lincolns and T-birds. Shoot two coats of pure acrylic enamel color. Let it flash for a spec amount of time. The paint remaining in the spray gun, use clear to refill the gun and mix it up. Shoot that mixture until it was used up. Then a final refill with pure clear for the final coat. The ultimate color match would NOT be exact until that final coat of clear was applied. This was well before any basecoat/clearcoat systems existed.
Many times, too, many body shops shot acrylic lacquer for repairs as it is less critical to dust, due to the way it dries. Which is also the reason it must be "finish buffed" for a good shine.
By contrast, acrylic enamel dries with a harder shine and needs to cure before it reaches its higher levels of durability. In those earlier times, a dust-free spray booth was necessary. Acrylic lacquer could be shot in an open shop, usually.
THEN came the "hardener" for acrylic enamel paints, as an additional additive. One of our painters shot a used car, a '76 LTD that was the silver metallic from back then. He shot it late one afternoon in our spray booth, with the hardener. The next morning, he backed it out and put the buffing wheel on it. I saw it later that day and it was "better than new money" glossy silver. That became the "new standard", to me.
Many people want to get their cars "patch painted" to get rid of door dings and rock chips, but the best option might be to get some paint mixed and then touch-up these areas, once cleaned with solvents and the edges smoothed, then using an artist's camel hair brush to fill in those recessed areas, in thin coats rather than one big glob, and then finish polish the area by hand. MUCH less intrusion into the factory paint that way and still achieving the desired smooth effect.
Paint is kind of like automatic transmissions, every painter has their own little tricks to get things done. Some "legal" and some "by their magic", it seems. I observed these and many other things over 50 years, your observations and experience can vary, which I certainly respect.
ENJOY!
CBODY67
