A screenshot of a Siri response with the following text: Each blackberry fruit is made up of multiple drupelets that are typically deep bluish black. The white bumps are most likely caused by heat or sun scald

Filing this under Siri is better than pundits will admit. Some parts of my blackberries are white (the individual berry bits) so I asked Siri "why are some of the parts of a blackberry white" and it came back with a real Siri Knowledge answer and a link to a page about White Druplet Disorder.