posts and pages layout

Single pages use a different template than archive pages. The separations are there, but they blend with the gray background. Remove the gray background color CSS and they’ll become visible. The gray CSS appears to be in your Additional CSS:

.site-info {
    background-color: lightgray;
...
}

Remove just the background-color: lightgray; unless you don’t like the other rules as well.

For me it’s important to have the footer of another colour than the body

Sure, but for some reason its color was bleeding over into the entire page. I’m not sure why. Something’s different now, it only bleeds into the sidebar now. I assume you don’t want your footer under the sidebar. To cause it to appear under everything, it needs to be cleared from all other content:

#colophon {
    clear: both;
}