what notes is the blues played in
Many are derived from the pentatonic scale. However, a true blues scale has what is called a blue note. A blues note means a drop in pitch located on the 3rd, 5th, or 7th tone of the scale. If this flatted note isn't included in the key signature, an accidental will be used to tell you to play that note as a flat. That scratches the tip of blues scales and there are many other variations.