16 Million Pixels (16777216 colors)

All 16,777,216 colors of 24-bit RGB palette (truecolor) in a 4096 × 4096 bitmap.

[16millionpixels]

16,777,216 colors of 24-bit RGB

All 16,777,216 colors of 24-bit RGB palette (truecolor) in a 4096 × 4096 bitmap. This image was made by zooming 

Image:Redgreen.png to 4096 × 4096 pixels

then adding 

Image:Blue256.png 

on every 8 × 8 pixels block of fixed red-green value.

more info 

https://commons.wikimedia.org/wiki/File:16777216colors.png