Red Spotted Purple
The red patches at this angle have an orange tint. None of these colors would be visible without the strong sunlight reflecting through the scales. To accentuate this I used some fill flash.
Thin film interference (TFI) is a result of selective wave cancellation. You may have experienced selective wave cancellation if you have ever used noise cancelling headphones. Some frequencies are cancelled while others are not. With TFI, as light reflects of layers of scale in the butterfly wings, some frequencies of light are cancelled out. What waves emerge produce the observed color(s).
Read about thin film interference at the TFI group.