As you have already learned, digital images are made up of pixels (with the exception of vectors), which are capable of displaying a certain number of colors. This number is known as a pixel's color depth or bit depth.
Color depth is defined by the total number of bits per pixel that can be displayed on the computer screen. Data is stored in bits. Each bit represents two colors because it has a value of 0 or 1. The more bits per pixel, the more color that can be displayed. For example, each pixel in a 4-bit image can display one of the possible 16 colors, while pixels in a 24-bit image can display one of over 16-million colors.
Images with a higher color depth obviously display much better than those with a lower color depth. However, higher color depth images are much larger in size and require more of your computers resources to display it accurately. In Paint Shop Pro, you can view your image's color depth in the Overviewpalette through the Info tab, and you can find out how many colors are used in an image by clicking Image > Count Image Colors.