An early butterfly in Indiana is the clouded sulphur, Colias philodice. These butterflies are nimble fliers and avoid predators. When disturbed, they typically fly a short distance, then drop into the grass where they are difficult to spot. The genus Coliascontains several species that will produce hybrids, including the orange sulphur Colias eurytheme.
The yellow color of the sulphur butterflies (which we can see) is due to the presence of the pterin pigments in the wing scales. The wings also produce a structural color due to reflected light in the UV range. (We cannot see the structural color because it is beyond the range of human vision). Presumably the structural color is visible to the butterflies that can see light in the UV range. The structural reflectance color is contrasted against the pterin pigment.
The clouded sulphur lays its eggs on clover. The larvae are dark green with white racing stripes along the sides. Like the cabbage white butterfly, the clouded sulphur also has four or more generations in Indiana. The adults fly until late in the fall. The host plants for the larvae, clover are available for much of the year.