I'm watching Steven Universe, and there definitely some things I'm noticing the second time through that I didn't notice the first time. For example, the song, "What's the Use in Feeling Blue" begins with three different notes that play in a specific order many times throughout the song. I think one of these notes was playing constantly during Blue Diamond's appearance in Korea, but I'll have to go back and confirm. All three notes played simultaneously during the corruption attack in Lapis's flashback, and the white light that appeared also had some hints of yellow and blue. I think that's the true nature of corruption. It's likely a special ability unique to the fusion of the three Diamonds, and the fact that Homeworld considers fusion only a tool of war means the Diamonds only ever fused during the war. That could explain why Peridot never knew about gem corruption until she came to Earth.