The blue pill and its opposite, the red pill, are pop culture symbols representing the choice between the blissful ignorance of illusion (blue) and embracing the sometimes painful truth of reality (red).
The terms, popularized in science fiction culture, derive from the 1999 film The Matrix. In the movie, the main character Neo is offered the choice between a red pill and a blue pill. The blue pill would allow him to remain in the fabricated reality of the Matrix. The red pill would lead to his escape from the Matrix and into the "real world". Wikipedia, Blue and Red Pill