There are multiple transformations of color signals in V1 cortex, and these different color mechanisms may contribute separately to visual perception of color boundaries and colored regions. There are single-opponent neurons that respond best to low spatial frequencies or large regions of color. There are double opponent neurons that are spatially tuned for colored and often also for achromatic patterns. The double-opponent cells are also tuned for orientation of colored and achromatic patterns. Finally there are color-blind neurons that sum cone input signals rather than subtracting as the opponent varieties do. Each of these types of visual neuron probably plays a role in color vision.