A colour scheme (or colour palette) refers to the group of colours you use in a project, a painting, or your living room. You as a designer usually picks a main colour and then chooses the other colours according to how they look together and the feeling they evoke when they’re viewed as a group. There’s a whole science behind picking colours based on what they mean to us humans and how they make us feel, as shown in the image below.
Those meanings and feelings can differ according to geographic location. For example, hospital rooms and public spaces are typically bathed in pale blue or green because those colours have a soothing effect, while Apple stores are predominantly white to reflect a feeling of elegance and simplicity.