Background color problems

I have a flash header with a light grey background color to match the background color of the web page. It matches fine on safari and firefox for my mac, but on my client’s pc, it’s a bright aqua color on exporer and firefox. Any ideas on what’s happening? The grey isn’t a web-safe color and I’m using it as both the document background and in part of the png files used in the file. It’s not live right now, but I can post a screenshot from her PC if that will help.