Touch-up problem

[Frodo]

Awhile back I had some doofus throw open his car door into my passenger side door, chipping out a very noticeable chunk of paint. It was irregularly shaped, bigger than the size of a pencil eraser, and down to the primer. I carefully sanded down the edges a bit, then layer by layer, filled the defect with touch-up paint, the real McCoy: Porsche seal gray. Actually over-filled it slightly, then sanded things down smooth. The color match, while not perfect, didn't seem too bad.

I then proceeded to layer on some clear coat, using some of the Dupli-Color clear that was layin' around the garage. This is where it got weird: After applying the clear coat, the touch-up paint seemed to mysteriously get much darker (see photo). Anybody else ever have this problem occur to them? I have no idea how to fix it, may just live with it. I've got some Dr ColorChip seal gray that actually matches better than this official Porsche stuff---thought about using some of it after sanding the current lesion back down, but I have no idea how much I'd need to take off. Any ideas welcome..

[Auf los!]

Your Porsche touch-up paint should have been a two-bottle kit, one the Seal Gray and a bottle of clear-coat. Why didn't you use the Porsche clear-coat?

I think your problem may be the old Duplicolor clear coat you used. Clear coat is funny and fussy stuff. It may have been too old to be any good anymore. Or the ambient humidity may have badly affected it.

I am currently trying to paint some Seal Gray parts using the Dr Colorchip paint airbrushed, and Express Paint urethane clear coat, and...the first clear-coat was fine, but the second was done with too much humidity, and it wrinkled up on me. Ugh. Gotta now sand-down and start over again.

[Frodo]

I had used the Porsche clear coat previously but, as I recall, had some trouble applying it smoothly (unlike the Dupli-Color, it's not an aerosol). I think I also recall having the seal gray darken some after it was applied, so I thought I'd go in a different direction clear coat-wise. Unfortunately I seem to have had a similar outcome.

I don't know how long the Dupli-Color clear should be good for, but I don't think it was more than 2-3 years old. It seemed to apply smoothly. The day was clear, maybe 70 degrees and maybe 50-60% humidity as I recall.

[woodsman]

Clearcoat ALWAYS changes the colour slightly. Your car's paint has probably faded
but a coat of white or silver under a fresh layer of seal may help matters. Certainly a translucent colour or pearl will change as layers are added. Does seal have a purple tint to it? If it does, than it's a pearl. What you are trying to accomplish can be quite difficult. It sounds like you have the patience to succeed.
Regarding clearcoats, the time between coats, or 'flash time' is important. Too soon and the first coat has a hard time drying, too late and the chemicals can attack the previous layer and wrinkling occurs. Mixing paint types can also lead to wrinkling for example painting lacquer over enamel.