What is 16M colors?
16M colors means 16 millions of different colours, even by just a little bit. Where does it come from? It comes from primary colour red, yellow and blue. But how can 3 colours become 16 millions colours?
Each colours will have 256 different colours shade. From lightest to darkest. So there will be 256 shades of blue, 256 yellow and 256 red. Multiply them together, it will be 16,xxx,xxx... Ok, it's 16,777,216.
From the lightest, 0, to darkest, 255 (why 255? because if you include 0, the total is 256 different shades), they will be mixed to get the 16 million combinations, hence, 16M Colors.
[If you play Final Fantasy VIII, you will realise the number 255 is quite familiar.... it's the max number of each attributes]
With so many different combination of colours, 16M colors phones will have better resolution, saturation and clarity.