Changing The Look Of A Disabled Button?

I've been tweaking a small AJAX login / user search page and I've run into a problem. I have three buttons, "Submit Query", "Add User", "Delete User" and a JS using DOM to modify everything on the login.html page.

I have a single external CSS file that controls the login.html page, buttons included. The way it works right now is the "submit query" button is blue, "add user" is green, and "delete user" is red.

In my JS file I diable the add and delete buttons if that user name already exists. Disabling the buttons is working correctly but changing the color of the disabled buttons isn't working. Here's what I've tried so far:

if( Name != null ){
b2.disabled;
b3.disabled;
b2.style="color:blue;background-color:yellow";
- or -
document.getElementById('b2').style = "color:yellow;background-color:yellow";
b3.style="color:blue;background-color:yellow";
- or -
document.getElementById('b3').style = "color:yellow;background-color:yellow";}}

I even tried adding a .disabled class to my css file:
#b2 .disabled{
color:blue;
background-color:yellow;
}
But nothing has worked so far. If you'd like I can paste all of the code, i.e. JAVA, JS, XML, CSS, HTML if anyone would like a working AJAX example.