Of all of the Google apps reworked to incorporate elements of material design, Calendar may be the slickest. It adopts the design paradigms of Android 5.0 Lollipop – bold colors, hovering widgets, and drop shadows – to great effect. That work extends to the in-app backgrounds; best viewed in tablet mode, each month features gorgeous artwork.
It would be a shame if the the images Googlers worked so hard to render remained locked within the Calendar app behind your monthly agenda. Thankfully, the good folks at AmongTech managed to extract and package all 12 for download.
To apply to your own home screen, download the zip file from the link below, then extract right onto your own device. They will appear in your Gallery, easily settable from there.
The papers make excellent home screen backgrounds, I must say.