The cloud, with its irregular forms, but with a pretty well defined contour, overlaps on the blue background of the sky lit by the sun that makes the cloud to gain new shades – from the white of the illuminated areas to the gray color of those shaded.
The picture was taken using a Nikon D40X camera with Nikon 55-200mm VR AF-S f/4-5.6G ED lens and these settings: exposure time – 1/640 seconds, focal length – 82 mm, ISO – 200, F- number – 5.