The theory posted on Reddit goes like this: In Thor: Rangarok, Loki gets into a fight with Tessa Thompson’s Valkyrie.
The theory is that baby Loki was able to see Odin’s memories, including his imprisoned daughter Hela, and he manifested his appearance to look like her.
When Odin first found Loki, abandoned as a baby on Jotunheim, Loki changes from his Frost Giant blue to Asgardian pink.
This memory magic opens up an interesting possibility.