Hue

• A butterfly may appear almost wholly purple, as in the luminous red-spotted purple of the eastern and southwestern United States. Or the hue may be a component of a more complex iridescence, as seen in the Florida purplewing.
  
  

Lighting

• The relative strength of ambient sunlight may affect a butterfly's appearance. Under pallid light, purple that almost glows in full sun may not come across at all.
  
  

Anatomy

• Learning the parts of a butterfly's wing can route your identification. Purple may appear on the dorsal or ventral portion of the wing; it may be part of the forewing or the hingwing (butterflies have two pairs of wings).
  
  

Characteristics

• Besides the purple color, look for other characteristics of the butterfly--including size, wing shape, flight pattern and the angle at which the wings are held in repose.
  
  

Field Guides

• A good butterfly field guide is an invaluable reference when identifying these beautiful insects, purple or otherwise. Some may be illustrated with paintings or drawings, while others--such as "Jim Brock and Kenn Kaufman's Kaufman Field Guide to Butterflies of North America"--may include photographs digitally altered to represent an average of diagnostic characteristics.