Hi CWMV
For accurate Colour Swatches go to SimmersPaintShop[link below].
This list is for U.K Aircraft Colours.
Look at box to the right of the colours called "Usage" and this will tell what this colour was used for.
There are a few FAA Colours listed so this may help.
To import into Gimp or Photoshop either use Colour picker or
what I do is highlight and Copy the "Hex" value [to the left of colour] and
Paste into "HTML_notation" Box in the Paint Toolbox of Gimp[or similar in Photoshop]
http://www.simmerspaintshop.com/page-RGB-colors-UK.html
Regards
Keith