Hot Pixel
A couple of days ago, I noticed a so-called Hot Pixel on some of my pictures. This is a faulty pixel in the camera sensor. In the magnification you can cleary see that there is something wrong, especially in the blue channel (from left: RGB composite, Red, Blue, and Green channels). It is also obvious that the final image is produced by way of interpolation from the sensor data, which means that the color values of each sensor pixel are partially spread to the surrounding pixels. This is rooted in the way the commonly used Bayer sensor is constructed, which I will not explain here (see, for example, Wikipedia).
At any rate, this is not a big problem since there is a Nikon Service Center here in Dresden which can solve the problem by re-programming the camera’s firmware. The hot pixel is “put out,” so to speak, and the missing information will from then on be gathered from the surrounding pixels. It is perfectly normal for a brand new sensor to have dead pixels, they are just programmed out right there in the factory.