The latest alpha release of device-cmyk just dropped, and it fixes a bug with the internal code that crawls CSS stylesheet rules for declared CMYK styles.

Long story short, this means it works with complex print stylesheets, like:

@page {
    background-color: device-cmyk(1 0.5 0 0.5);

    @top-center {
        background-color: device-cmyk(0 1 0 0.5);
        content: 'HEADER';
        display: inline-block;
    }
}

Try it out!

Remember, all you need to do is include the polyfill on your site, and voilà, CMYK colors work!

<script src="https://unpkg.com/device-cmyk@latest/dist/device-cmyk.polyfill.js"></script>