custom background with transparency

hi,

I am looking for a possibility / plugin to use for special categories on my site different background images…

moreover I would need to adapt the content part of my website to a white background or “half transparency” – like it is done here https://reface.me/wp-content/uploads/facebook-timeline-red-bull-1024×800.jpg – so that the background image is better visible but also the content good to reed.

does anyone have a solution for this to realize…

thanks, bergblume