When I sat to review & fine-tune my Calibre library in February, I also have decided to make a Penguin-inspired book cover template! Shows, that they are truly a classic designwise.
My version is very minimal, and I've made 36 colour-variations to choose from.
Available in SVG & PNG format, with instructions on installation and SVG editing for even more colours.
Can be downloaded here:
Calibre Book cover templates (Penguin)