Opaque paint does not allow the light to transmit through the paint. This is important for covering imperfections and for retention of true color in many instances. For example a transparent yellow painted over a blue will look green, whereas an opaque yellow, such as Cadmium Yellow will happily cover the blue and yet still retain its yellow hue. The traditional method of oil painting called for the first layers of a picture to be thin, dark, and transparent. Opaque lighter layers of color were then painted over this to give a sense of solidity to objects.