Your television only produces three colours. Those are the three primary colours of light red, blue and green. It produces them in tiny little dots can't be seen individually by the naked eye. The effect being that the colours will mix together, the intensity of the red green and blue dots is varied to produce all the colours you can see. The white blob you see on the screen is actually composed of small red green and blues dots. if you put a VERY small amount of water on the screen the water will act like a lens enabling you to see the dots individually. Moving the mouse over the spot will also maginfy the dots for you (but more so).

there is also no true black on a T.V. The darkest you can get is that the grey that you get when you turn off the T.V. You are fooled into thinking its black by the relative brightess of the surrrounding colours. If you get a black card and cut a hole out and place it over a black area of the screen you will see that for most screens it is just grey (There are however some expensive screens that can produce quite a black screen nowadays, espiecally on laptops.)