As an interior paint color consultant I think mixing patterns creates dynamic and fascinating spaces. It does not appeal to all. For some, it makes a space less harmonious and therefore less peaceful. If monochromatic minimalism is your aesthetic it just won’t work for you and that’s OK. For we who love interesting juxtapositions, if done right, 1 + 1 will equal 3 by combining diverse patterns in one space. Though there are some good general guidelines, many people who possess the skill of combining patterns effectively do so intuitively. A master of it is the Interior Designer Muriel Brandolini. She is fearless when combining color and pattern though her designs might be considered on the bolder end of the spectrum.
The two biggest factors to consider are color and scale. The rules regarding scale are less flexible than those which guide color. Successfully mixing patterns require using patterns of very different scale together. Large, small and medium prints work best when combined. If you stick with all one scale in a room you will overwhelm the space and create an environment which seems both over stimulating and boring at the same time.
There are many approaches to choosing colors when combining patterns in one room and all of them can work well. You can use a limited color palette of just a few colors in all of the patterns you choose. This will give you a more controlled feeling in the room. You can use a solid color as your field or background color, for instance using white walls, then use multiple patterns in the rugs, throw pillows and textiles of the curtains and upholstered furniture. It’s safest to include at least one large scale solid in the room, be it the walls or a sofa, for instance. Tying the colors together through their relationship to one another can help the cohesion of the room. Using predominantly different shades of the same hue with added accent colors will work. Choosing analogous colors which sit next to one another on the color wheel or complementary colors which sit across from one another, will help create a relationship between the colors in the patterns and unite the room.
Still, there are those who are able to put myriad patterns containing many, many different colors together into one room and it just gels. Some things just work and it’s senseless to try and decode why. Here are some nice examples of mixing patterns.