Well, actually there are, roughly speaking, two kinds of "Ghost" paint-jobs: the ones that were painted here in Greece at the HAI paint shop and the original, factory-standard paint-job.
Having said that, the other major contributing factor is "time since paint was aplied". The old block 30 Vipers and the F-4E AUPs get a new paint every, say, 5 years. However the block 50 Vipers are still wearing the original paint after all these years. Its easy to see looking at the pictures how the elements have taken their toll.
HTH