The Matrix: Red vs Blue Pill (part 1)

The red and blue pill are visuals used by rebels inside the matrix to make potential rebels choose between remaining plugged to the matrix or being freed. Morpheus offers Neo the choice between blue or red pill during their first encounter.

He explains that taking the blue pill will make Neo wake up in his bed without memory of the last events, believing whatever he wants, while the red pill would keep him inside the real world, unplugging him from the matrix that imprisons his mind.
Quote: "This is your last chance. After this, there is no turning back. You take the blue pill - the story ends, you wake up in your bed and believe whatever you want to believe. You take the red pill - you stay in Wonderland and I show you how deep the rabbit-hole goes" (Morpheus).
Hence, the blue pill would keep the person unaware of its actual state of being plugged to the matrix.
Cypher, the rebel and crew member of the Nebuchadnezzar, who will become a traitor, once utters to Neo: "I know what you're thinking, 'cause right now I'm thinking the same thing. Actually, I've been thinking it ever since I got here. Why, oh why didn't I take the blue pill?