‘Mukherjee went out with the intention of snapping pictures of the ISS transit of the sun. However, due to some unexpected clouds blocking the sun, he was forced to abandon that plan…The colors in plane contrails are due to individual water droplets diffracting sunlight. When the droplets are equal in size, they diffract colored light in the same direction, which in turn makes the hues visible to humans…Each image is actually a composite of seven individual images captured over a period of 40 seconds. As a result, each photo depicts the changes in the iridescent colors and shape of the plane contrail…’

Found here and his Website