How to change Checkbox color according to a certain condition?

I must admit i am a newbie in web development. I am working(Practicing) on Bus seat reservation system. I am displaying seat layout using checkboxes to allow user to select seat. Styled checkboxes to look like a small square which shows up in color 'X' if unchecked, else 'Y'. I want to display unavailable seat with color 'X' and available seat with color 'Y' right at the loading of the webpage. Availability will be obtained from DB.

I have no idea how to accomplish it. It would be so helpful if someone could assist me.

Thanks in advance.