Apparently Boeing have in their employ a few "artistic" painters who do the 'one-off' color schemes on the tails... e.g. China Airlines Cargo with the flowers, or as someone mentioned, things like the Frontier animals....
Seems it's a combination of handpainting and spraygun use, depending on the level of complexity in the logo.
All that I saw were using proper suits/breathing apparatus. Quite interesting to watch actually!
Sky