There are thousands of plant combinations, companion plantings, and color combinations that will work well in landscaping and garden planting schemes.
And form a beginner or do it yourselfer standpoint, simplicity and repitition in planting is a good starting point that can be added to later. I usually say to pick a color scheme of two or three colors and repeat it throughout the garden.
For more curious, experimental, or advanced home landscapers there may be a feel for planting in masses or even random, assorted, and wildflower and ornamental grass beds.
In any instance, there's always a chance that even the best of planting intentions can disrupt harmony, balance, and unity in the garden instead of creating it.
Periodically adding a neutral colored plant throughout your landscape can help unify planting beds that differ in color, texture, and even height.
Silver or gray plants such as Lambs Ears, Artemesia, Dusty Miller, Santolina, Sage, Horehound, and others are considered neutral colored.
Using white flowers as a neutral also works very well. Anything white is a natural focal point and especially in the garden. In a mass of green foliage, orange flowers, mixed flowers, etc., white always draws our eyes to it. Using it throughout the garden will create a sense of unity.
Use white sparingly. Too much of it tends to feel cluttered.
Unifying a garden that's out of sorts is really quite simple. As well as moving and matching existing elements, try adding a neutral color plant to the different planting areas.
Separating or "buffering" beds from each other can be as simple as adding a neutral or group of neutrals between colors or beds.