But What Does Purple Mean?

Camryn is in preschool and is learning what the colors of the stoplight mean. The teacher uses the stoplight in her class so the kids know if their behavior is good or needs some work. Every day Camryn says "mommy, green means go, yellow means slow down and red means stop." I tell her "good job." Then she always asks me "what does purple mean?" I always say it is not a color on the stop sign but just a pretty color on the rainbow. That satisfies her for about 2 minutes and then she starts all over again and ends with "but what does purple mean?"

If any one has any suggestions, please let me know! She is not satisfied with my answer:)