Any color which appears in the visual field will automatically cause the viewers mind’s eye to seek out the complement of that color.
Until the mind’s eye finds the complement of a color, it will continue to search for it. This can cause the eye to dart quickly.
If the complement is found the mind’s eye is satisfied.
When the complement is not found the mind’s eye will produce it.
This is why good design needs the balance of harmony to satisfy the mind.