The color of the room which is to be painted depends on the amount of light which enters the room. The light entering the room includes the direct sunlight and the reflected light (for example: if there is lawn outside the room, light will reflect from the green grass and enter the room).
So choice of the color to be used has to be made keeping these things in mind. The orientation of the room also plays an important role in deciding the color of the room. As rooms facing east and north receive less sunlight so they are darker hence require chilly colors. While rooms facing west and south receive more sunlight hence require cool colors.
Hence as a thumb rule, before coloring the room, first find out the direction from which light comes in and goes out. One more thing which has to be kept in mind is that, color of the room changes throughout the day due to variation in the radiation of sunlight.
At Mid-day room becomes blue, while at dawn it becomes pink and at evening it turns out to be purplish-red. The geographical condition of the room also effects the color to be used in the room. Color of the room also depends on the utility of a space.
Busy family kitchens should use cool relaxing colors. Trendy singles can take more drama, so they can be painted in bold colors. Bright colors not always work for bathrooms. Bedrooms should use warm colors like orange, yellow or red for a good night sleep. Rooms/ Spaces which get less use can be painted in strong colors like strong red or yellow.