I am creating a contact form for my website and and using javascript to the first layer of validation before submitting it which is then checked again via php but i am relatively new to javascript, here is my script...

$("#send").click(function() {
    var fullname = $("input#fullname").val();
    var email = $("input#email").val();
    var subject = $("input#subject").val();
    var message = $("textarea#message").val();
    if (fullname == ""){
        $("input#fullname").css("background","#d02624");
        $("input#fullname").css("color","#121212");
    }else{
        $("input#fullname").css("background","#121212");
        $("input#fullname").css("color","#5c5c5c");
    }
    if (email == ""){
        $("input#email").css("background","#d02624");
        $("input#email").css("color","#121212");
    }else{
        $("input#email").css("background","#121212");
        $("input#email").css("color","#5c5c5c");
    }
    if (subject == ""){
        $("input#subject").css("background","#d02624");
        $("input#subject").css("color","#121212");
    }else{
        $("input#subject").css("background","#121212");
        $("input#subject").css("color","#5c5c5c");
    }
    if (message == ""){
        $("textarea#message").css("background","#d02624");
        $("textarea#message").css("color","#121212");
    }else{
        $("textarea#message").css("background","#121212");
        $("textarea#message").css("color","#5c5c5c");
    }
    if (name && email && subject && message != ""){
        alert("YAY");
    }
});

How can i write this more efficiently and make the alert show if all the fields are filled out, thanks.