Function which takes 4 arguments: 
1) The HTML element. 
2) The color to be switched in. 
3) The color to revert to (the original color. 
4) The font color to be switched in. 
5) The font color to revert to (the original color. 
Sets the speed of the changed to 400ms. 

Could easily be changed to a "toggle" effect by replacing 'hover' with 'toggle'.