Let's just say you have 3 buttons:
<input type="button" disabled="disabled" value="hello world">
<input type="button" disabled value="hello world">
<input type="button" value="hello world">
To style the disabled button you can use the following css:
input[type="button"]:disabled{
color:#000;
}
This will only affect the button which is disabled.
To stop the color changing when hovering you can use this too:
input[type="button"]:disabled:hover{
color:#000;
}
You can also avoid this by using a css-reset.