On the difference between science and pseudoscience, Mach's dictum "where neither confirmation nor refutation is possible, science is not concerned" still applies.
If it's not possible to know with certainty that an example (e.g., a black swan) disproves a hypothesis (e.g., "all swans are white"), then it's not a scientific hypothesis.
This means hypotheses need to be expressed with zero semantic ambiguity, which necessitates expressing them in a formal (mathematically precise) language
Dawlish in Devon, UK is famous for it's black swans, I am sure that someone must have at some point researched this collected, DNA from both white and black swans to determine if black swans are a distinct species or the same. (I am not sure on the right vocabulary). So there may be some research in to this.
