Really fun game! I used VGVubmVycw== to solve it, but I think I misunderstood how Yellow worked. The rule I came to the conclusion was dGhhdCBpdCBoYXMgdG8gaW5jbHVkZSAiRVJTIg==, but if a word like cG9wY29ybg== works, that rule completely goes out the window.
(Every instance of jumbled text is Base64.)
Edit: Oh wow, I think I know how Yellow works now, and I misunderstood it more than I originally thought. Huh.
also apparently someone made a regex, so try to decode this: 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.
Have fun!
