This was taken during our September 2009 trip to Washington, DC; actually in the herb garden of the National Cathedral.
The whole garden was swarming with butterflies in the September sun, which was unseasonably hot. There were lots of these ranging in colour from pale cream through canary yellow (as this one) and pale green and pale orange. Don't know if they were all the same species, but they all looked the same apart from the colouring.
And there were also lots of Monarch butterflies and several delightful hummingbirds, which I totally failed to be quick enough to capture.