Color noise are fluctuations of patches of colors in your image. Also know as chroma noise, it is usually more unnatural in appearance and can render an image unusable.
Noise is caused by taking a photo with a high ISO setting, underexposure (not enough light), or by shooting in a dark area with a very long shutter speed (for example, a 3 second exposure). The reduce noise command can correct this to some extent. Choose Filter > Noise > Reduce Noise.
reduce noise command to carefully reduce both noise types individually while retaining the most amount of detail.
