This is a colour bar, ranging from magenta, over blue, green and yellow to red (kind of like a rainbow). You should be able to see a smooth transistion from each colour to another. If you see little dots or odd looking stripes in this bar, your computer doesn't display the full colour range you could see.
This is a greyscale picture, showing seventeen shades of grey. You should be able to tell apart each of the seventeen shades from the neighbour-shade, if this isn't the case, you might need to change the contrast and the brightness of your screen until you can (usually the shades that matter most are the three leftmost and the three rightmost ones).