Color plays an important role in the perception of a space in mind. Using lighter shades makes space appear bigger while darker shades makes the same space appear smaller.
Hence colors can be used appropriately to adjust the proportion of room. For example: For an extra-ordinarily large room, using dark color will make the room feel small and cozy.
If a room has a coving or cornice, then painting the wall and the coving in the same color will make the walls look higher and the room area look smaller whereas painting the coving and the ceiling in the same color will make the room area larger but with a smaller room height.