Anyway, if you look at the generated HTML you will see a series of option tags. So what you need to do is set the background color for the desired option tag. You could do this by applying a style based on the tag id.
Please be sure to ask Struts questions in the Struts forum. I have moved this post there for you.
Also, please be sure to use code tags when posting code to the forums. Unformatted or unindented code is extremely hard to read and many people that might be able to help you will just move along to posts that are easier to read. Please click this link ⇒ UseCodeTags ⇐ for more information.
Properly indented and formatted code greatly increases the probability that your question will get quicker, better answers.