When it comes to choosing "cool" colors or "warm" colors for your room design, it should depend on the intent of the room. Cool colors like blues are said to have a calming effect and would work best for a bedroom, meanwhile warm reds, oranges, and yellows are said to make a room feel cozy, much like a fireplace in a living room would.
The Color Wheel
The color wheel in color theory is divided into warm and cool colors. On the cool side of the wheel are shades of green, blue, and violet. This includes bright green, blue-green, ocean blue, cobalt, as well as shades of purple and violet.
Like water, sky, and greenery in nature, these colors are soothing and bring a sense of calm to a space. These colors also give the impression that they are receding. They make a space feel more open, adding to the serene effect. Trendy gray is technically neutral, but it can be a warm gray or a cool shade. If it's a steely, bluish-gray, then it acts as a classically cool color.
The decor rule of thumb is that opposites should enhance each other. In the color wheel, these are called complementary colors.
Cool and Complementary Colors
Start with a neutral background—shades of white, taupe, gray, or beige. Keep it on the light side. The safe money is on also keeping your furniture and flooring neutral so that the expensive parts of your room can look good with a multitude of changes in the color scheme. Or go bold, if you have deep pockets, and let the upholstery pop.
Now, think about complementary colors on the color wheel. For example, pair a soft greenish-blue area rug (cool) with burnt orange (warm). Consider greenish-blue and burnt orange patterned or striped throw pillows to accent a room of neutral cream-colored walls, hardwood flooring, and a neutral-colored sofa. Ideally, the pillows can tie in with a rug, and the orange accents pop against a neutral sofa or walls, adding some color drama.
Or, use eggplant (cool) and pale yellow (warm) for a striking combo in a bedroom or bath. For the bath, paint the walls a very light shade of yellow for cheeriness and add a cream-colored ceramic tile for a neutral base. The vanity can add warmth with its wood tones and use eggplant as an accent in towels and wall hangings.
For a bedroom, paint the walls a creamy white. Dress the bed in creamy neutrals for a peaceful canvas and add throw pillows in soft yellow and eggplant, using patterns or stripes of both colors. Toss in some solid eggplant throws for a strong accent. Or make a strong statement with an eggplant duvet cover and shams, accented with cream and a bit of light yellow in the throw pillows for warmth.
Go for a monochromatic cool vibe by using several shades of the same color along with a neutral. Various shades of blue used liberally as accents in an otherwise all-white room are quintessentially cool. It makes for a peaceful bedroom. Use a palette of greens for a fresh and stunning bath that is set against white tile.