Color can be described as cool or warm depending on its position in the color spectrum and the hues of its nearest neighboring color.
Warm colors project the hot hues of sunlight and promote a feeling of warmth in a room. Cool colors can increase the perception of space and are used to make walls appear closer. Cool colors are violets and blues.
Red, orange and yellow are warm colors, while violet and blue are cool colors. Green is said to be a neutral color.