$(document).ready( function() {

    $(".diagrams").children("div").hide();
    
    
    if ( $(".diagrams").children(".diagram1").length == 1 ) {
        $(".diagrams").children(".diagram1").fadeIn("fast");
        $(".diagramButton:first-child").css("color","Green");
    }
    
    
    $(".diagramButton").click( function() {
        $(".diagrams").children("div").fadeOut("fast");
        $(".diagramButton").css("color","Black");
        
        $(".diagram" + $(this).html()).fadeIn("fast");
        
        $(this).css("color","Green");
        
    });
    
    

});