First a suggestion. Since you use a lot of images, reduce the number of posts you have on your main page to perhaps 5 instead of 10 at settings > reading. Your site will load faster and that will make your visitors happier.
Right now your main column is so wide that you may as well just do away with the sidebar as it will be unusable at 100px wide which you can see for yourself by putting the following into your CSS and then viewing the site.
.secondary #main .widget-area {
width: 100px;
}
Background color for the widgets is here. Just edit the hex color code.
.widget {
background: none repeat scroll 0 0 #FBFBAD;
}
If you want to get rid of the sidebar, do the following and then widen your main area to the full width.
secondary #main .widget-area {
display: none;
}