The "Magic L" uses I - IV - V chord progression. Which mans that all the chords are either major or minor, depending are you playing in a major or natural minor key. No mixed major/minor chords in that progression.

Some examples:

Major: C - F - G

Minor: Am - Dm - Em

(Having said that, harmonic minor is an execption, it has major V chord in it. But, I think you aren't that far yet on the theory.)