Colors make an image sing. Color relationships make an image harmonize. The image below has a powerful border of teal, from the paint on the wall behind the mirror, which makes a strong warm/cool color relationship with the gold of the mirror frame. But the further relationships of the gold of the mirror frame to the similar gold in the painting frame in the reflection, and the wood tones of the frame relating to the wood in the reflection, tie the layers of the image together.
C. David Tobie