Semi transparent background of content area

Hello,

first of all I want to say, that I absolutely love your theme, great work!
I have a short question regarding the content area. I have a big background image, and for the content areas I want to have a semi transparent background in white, so that the background image also shows through the content area a bit.
I already set the colour of the background for the content area to zero, but than I have no background and the readability of the text is difficult, because the big background picture is quite colourful. So by having a semi transparent content area background in a white tone, with a black font the readability would be much better and it will also looke nicer I think.
Now I wanted to ask, if this is possible?
Thanks a lot – I would really appreciate your help!

Colin