Can we set background color for a button in runtime?

Hi,

In my application, I have one action button called "Upload File". When I click on it, it allows me to select file from my system. Now, after adding a file I want to change the back-ground color or button color to green. As an indication for we already uplaoded a file. Can I approch this?? Can any one please help me. Or else give me suggestions to identify that the file is already uplaoded.....  

Thanks & Regards,

Venkat.