Portfolio grid complete container background colour

Hi, I wondered if you could help me with a problem I’m having with full width portfolio grids.
I want to have a completely white background including the categories menu. My main site colour is a dark grey and where there are gaps in the thumbnails text when the browser window is re-sized you can see through it and see the dark grey in places.
see this near bottom of page http://fullrotation.com then resize the window width

I’ve styled and colored the title background text colours etc no problem with this code

.grid-entry .main_color .avia-arrow, .main_color .grid-content { background-color: white!important; color: white!important; }
.main_color .grid-entry-title { background-color: white!important; color: #3f3f3f!important; }
.grid-entry .inner-entry { box-shadow: none!important; }

…. but I need the whole portfolio grid background to be white

please see this image to help explain

Now, one fix would be to put it in a full width color section with background set to white. I tried this and creates two problems
1) The categories menu is now not centered, it stuck to the left of screen
2) the color behind the categories text is still dark grey.. I used this to change it to white

#js_sort_items a {
    background: none repeat scroll 0 0 white !important;
}*/

But it then left little dark grey squares in between each title

SO there must be a way of doing it without putting in a color section and I’m just not getting it
Many thanks