Add_ALPHA_Value_to_Base_Graphics_Colour.R

## Add an alpha value to a colour
add.alpha <- function(col, alpha=1){
	if(missing(col))
		stop("Please provide a vector of colours.")
	apply(sapply(col, col2rgb)/255, 2, 
		  function(x) 
		  	rgb(x[1], x[2], x[3], alpha=alpha))  
}