0
You can manipulate virtually all elements of the screen just by inspecting elements with firebug or browser tools themselves, an example if you wanted to change error messages, it would be:
.ui-growl-error, .ui-growl-fatal, .ui-messages .ui-messages-error, .ui-message.ui-message-error, .ui-messages .ui-messages-fatal, .ui-message.ui-message-fatal {
background-color: #FFFFFF;
border-color: #red;
color: #000000;
}
This is the part that I dislike the most in these faces Beans, always need to overwrite the CSS, and often needs to be forcing the CSS to use the property with ! But anything can be done.