Touch-up problem

[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.