Triad pairs make pretty patterns that can make good sense and stretch over more than a couple of measures.
The idea is to pick two traids from a scale that don't repeat notes.
Usually that's done by choosing two a whole tone apart.
Interestingly you can deliberately choose a triad that falls a little outside the tonality.
At least for one note. Eg: In C major - Lets mix up C-Major and D-Major, even though
a D-minor triad would have all it's notes in the scale of C major. D-major triad has an F-sharp!
This not is the tri-tone or blues note and makes a pretty colour.