This clouded yellow butterfly kindly stopped by for a photograph as we were exploring an old film set at Big Bend Ranch State Park, Texas. These are of the genus colias, of which there are many variants. They are apparently called ‘sulphurs’ in North America.
You can see the apparent shading on the wings, where the strong dark outer colouring on the top of the wings shows through. A web search shows that these butterflies are not often caught with their wings open to reveal the upper side. Here’s an example male (upper) and female from Wikipedia. We can infer that mine is a male.