[Markus]

Thx for the info!

Just to clarify: you have set the background image of a post and this is showing up in the gallery? i just noted that you only have one image. does your method also work with a gallery?

I tried setting the background image of 5 (featured) posts using wp-background lite plugin. this didnt show up – even after increasing the z-index in the plugin to -1.

i also tried unsuccessfully setting the background manually in css like

body.page-id-317 {
background-color: #000000;
}

thanks for any info on this.