A riff, run, or any other facny name is nothing more than a piece of a scale or a broken chord. It can be from any scale (major, minor, blues, pentatonic, etc.) or chord (major, minor, augmented, diminished), it doesn't matter. The key to most runs is to play them fast using the correct notes to make it seem like you are hitting random notes. Most people would say, "Man he just hitting any old notes," but in reality the musician knows exactly what notes to hit and how to hit them. Example:
Key Eb RH only
Play very fast: Gb, Ab, Bb, Ab, Gb, Eb *this run is usually associated with preacher chords
Gb, G, Bb, C, Eb
Gb, A, C, Eb, A, C, Eb, Gb C, Eb, Gb, A Eb, Gb, A, C *fully diminished chord being played in arpeggio form