Originally Posted by: larsm2011There you can see that the e chord is in there but it is a minor the ii,iii and vi are minor in a major key

Thanks for your helpful reply, Lars. :)

All of this info about which chords are in a key are covered in my music theory tutorial. Conveniently, the example is in the key of C major.

http://www.guitartricks.com/tutorial.php?input=495

Also, an example of an accidental, using a chord with notes outside of the key are covered in this tutorial about basic improvization.

http://www.guitartricks.com/tutorial.php?input=876