Because the elements that have a higher EN can seize ilektron from the elements with lower EN colors have come out to be the color of the element's ilektron.
For elements with EN higher than the car to steal electrons from the elements with EN under the colors come out in the color of the elements were deprived of their electrons.
Because the elements with higher EN can steal from EN electron elements with lower color has turned out to be the color of the element being replaced ion.