How computers creat colors?

First of all the computers use the Hexidecimal system (explained in the previous bolg) to creat the colors and then show it in the monitor.Actually the computer uses only three colors to make 16581375 color (each color has 255 ; the 255 is FF in hexdecimal different value 255*255*255= 16581375) by mixing them together. These colors are RED, Blue, and Green.