|A developing pod on Aberrant Angela's Blue|
A, Pu and Pur, the three genes needed for purple podding are dominant. Whoever bred Angela's would have had to select for purple podded phenotype from their original cross. This means the plants they selected from would have had to be carrying A, Pu and Pur. But you can't tell if the plant has one copy of the dominant gene (heterozygous) or double copies (homozygous) unless you grow out lots of the progeny. My guess is the original parent was heterzygous, was grown out for a number of generations until the breeder thought it was homozygous for all three genes, but lurking in the population from which the seed was collected was a plant which was heterozygous for either Pu or Pur.
This is what a purple podded is supossed to look like: