UIMarkupTextPrintFormatter PDF creation with custom background and transparent HTML content

This isn't a guarantee, but as Yvonne mentioned, it's possible that your PDF renderer just doesn't support transparent as a color value.

Possible Solution A

Try creating a 1px by 1px PNG image with just one 100% transparent pixel, then set that as a repeating background image on your element.

Possible Solution B

It's possible that the HTML element itself is white when this library renders it. You can apply CSS to the html tag the same way you did with body.

Possible Solution C

If I understand your case correctly, you're trying to overlay a rendered PDF which is inside of a UIWebView on top of other in-app content. I can't speak to whether a PDF can really support transparency. The UIWebView may have its own properties required (not to mention there may be a PDF viewer with a default background of white in play). If you have control of the UIWebView's styles, take a look at this: How to make a transparent UIWebView

Possible Solution D

Maybe it would be better to use a Canvas (either HTML or Switft) to render an image instead of a PDF. If this works for your use case, it may be a much better option long-term.