ImagickPixel is the class that represents 'colors' in the underlying ImageMagick library, or more precisely reprensent a pixel in the color space that the image is in.

For RGB colorspace this is indeed a color, for other colorspaces/images the meaning is slightly more ambiguous. For example if you convert an image to HSB (hue, saturation, brightness) and then split the H channel into it's own image, the ImagickPixel in that image will just represent hue.