How to change item's style at run-time using J2ME Polish

How can I change item's style at runtime using J2ME Polish?

I'm trying the following code but I'm unable to get it wo开发者_StackOverflow社区rking.

Style style = new Style();
style.addAttribute("background-color", "#FF0000");
item.setStyle(style);

Style style = new Style();                        
style.background = new BorderedSimpleBackground(0xF0F0F0, 0xFF0000, 1);
item.setStyle(style);