So, I used the following in custom css and made the background fully transparent:

#header{
background-color: transparent 0.85;
}

Unfortunately, it also makes the menu hard to see – specially when the background is a slideshow. Is there a way to adjust the level of transparency of the header?

thanks for the response.
actually i meant that if for example i have 10 images, is there a way I can use those 10 images to create a full page slideshow and use it as a page background which also goes behind the header and the menus?