<< Why are LCDs only 16.7 million colors? Is'nt that 16 bit? >>
No, these are the common colour levels availiable for CRTs and LCDs. Note that many new OS wont let you select most of these, infact 8,16 and 24/32 bits are often the only ones allowed.
1bit = 2 colours
4bit = 16 colours
8bit = 256 colours
15bit = 32,768 colours (32K)
16bit = 65,536 colours (64K, or High Colour)
24bit = 16,777,216 colours (16.7M or True Colour
32bit = 16,777,216 colours plus a 8 bit alpha chanell (also called True Colour)