Just throwing in my two cents here. I legally have to include a printed receipt with every package, as my products are subject to inspection by the department of agriculture. In this setting, it's pretty nice to have branding on the receipt to identify my company consistently with branding elsewhere on labels. As you've already mentioned, our white logo doesn't appear well on printed receipts. I would be totally happy using a header background color as opposed to an image substitution as well.
We print directly out of the Squarespace platform without any 3rd party integrations, primarily using Google Chrome.