So here's the story, I recently picked up a batch of USA FDC's for dirt cheap. USA isn't very popular here in Europe. And I noticed a few things seemed 'off' on some stamps. So I did some research but couldn't find anything concrete. They look like errors.
So anyway, here they are. If anybody can help me with this I would be very gratefull, Thanks in advance.
Here are they
 Banking se-tenant from 1975; I can vaguely remember that the native American cent was bronze, and the big coin right looks half coloured.
 First solo flight across the transatlantic 1977; Isn't this stamp more as a night sky ?, seems some purple is missing
 Pap test 1978; The left stamp seems to only show the slate
 Honouring Herkimer from 1977; I don't know what to think of this one. Red omitted, stamp put in sun ?
 Frank Lloyd Wright and American flag from 1959; Red omitted from USA flag
 Rural america from 1977; red omitted in combination with a normal one
 Jimmy rodgers from ????; Left one shows purple, right one doesn't. and Jimmie ... Looks a little pale
Thanks again :D