Casper background color: from trasparent to white

i’m new to Casper.
I use a installation.
My grafic designer help me to build logo and banner.
When I put the banner that has a trasparency the background is grew or in other solution black.
I want to see with as I can see in graphic software.
This is the site and I attach the banner

I also want to see the menu bar in white color in the other pages and not black