Background image not correct colours?

When I upload a new bg.jpg image it is not showing in the correct colour is there some overriding CCS that gives the image opacity or something similar? I have used the same colour in the logo.png and this displays fine, any help would be great as I can see no reason why the exact same colour would display differently.

If your website is online can you post a link in here so we can check. Thank you.

See you around...