Yellow Tulips Develop Red Streaks

What would cause my yellow tulips to develop red streaks?

You didn’t do anything wrong. Color changes like these are common. They’re usually the result of a virus, an environmental response or a genetic mutation. In fact, it was a virus that caused the streaked tulips that resulted in the Tulipomania craze in Holland in the 1600s. I suggest you just enjoy this garden surprise and wait to see what appears next season.