Red, orange and yellow are warm colors, as they reflect the colors of the sun, fire and daylight. In artwork, warm colors are used to stimulate observers, and in interior design, warm colors appear to come forward, which can make a room feel more comfortable.
Cool colors are the colors from blue-green through blue-violet, including shades of gray. Blue, green and purple are the most prominent examples. Cool colors are associated with the ocean or an overcast day, and they are used to calm and relax the viewer. Cool colors also tend to recede in an interior design setting, so they can be used to make a room seem larger. In order for psychological and physiological color effects to work, they need to be contrasted with an opposing warm or cool color with a higher saturation and lighter value.
Some shades of the same color can be warmer or cooler than others. If a color shade has undertones of red, orange or yellow, it is considered to be warmer than the same color shade with undertones of blue, green or purple. The undertones of a color are what give it its relative temperature. While an orange shade is always considered to be warm, there are varying degrees of warmness when compared to another warmer or cooler shade of orange.