Harmony happens—and not always from inherently harmonious pieces.
Bright sun pierces through the new leaves of the purple-leaved smoke bush. The surface color of leaves' non-reflecting "flat-matte" burgundy actually contains the frank and un-nuanced red of the very young Hino Crimson azalea in the back.
So far so good, but imagine when the Hino Crimson is more mature, in a decade or so, six feet tall and eight across. The darker leaves of the smoke bush will be like sunspots on the sun: points of darkness barely visible with the smoldering brightness to the back.
But garden harmony doesn't end with the intentional pairings, let alone the permanent ones. The red plastic milk-crate cube—which I've had since the mid-Seventies when I, uh, "acquired" it when furnishing my first-ever aparment, in downtown Baltimore, largely off the street—
and was nearby only because I sitting and standing on it when doing some pruning just out of frame, is also getting down with the azalea and the smokebush.
And the two galvanized garbage cans, which I keep filled with well water to warm up in the hot Summer before I dip my watering cans in, are an excellent grey backdrop for everyone.

Good combinations are good regardless of their elements. The point is that it work, whether by chance or by intent, for the afternoon's work-session or for decades to come.