When soloing over a chord progression containing a major chord which is out of the key, use a Lydian scale. For example, if your chord progression in the key of C is C-G-F-Ab, it is clear that the Ab chord does not belong to the key, therefore using C Major to solo the entire way will not work. So, use the Ab Lydian scale over the Ab chord – you will find some interesting ways of getting in and out of Ab Lydian in a C Major solo.
For minor chords out of the key, I generally choose Dorian.
Try it out. Record a progression with one chord “out” and test your ability to change scales mid-solo. Have fun!
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