Grayscale: Each pixel supports 256 shades of gray from pure black to pure white, using numerical values of 0 to 255.
Convert your loaded image to grayscale and examine it. Move your pointer over the image and watch the pixel values in the Info window. Note that red, green, and blue are always identical. (That makes the color a gray.)
Now, use Undo History in the Palette Window to undo this conversion.
