/Mailspring Inverse Images

Created Mon, 09 Jan 2023 22:19:57 +0000

Inverse Images in Mailspring

So I run most apps in darkmode, and this can lead to a few issues, namely in Mailspring which does darkmode in the “easy” method, which is to inverse(100%) everything now this makes general emails really easy, the problem is when you get to images, because inversed images are horrible to look at

So I got bored over new year, and decided I was sick of looking at them, and because I use Dracula for everything, I set off on my journey


Now Dracula is an awesome set of themes, that has pretty much support in every app that most devs use, if it doesnt then its probably coming soon


Mailspring is an email client that was started by the people who did N1, which is another mail client, the reason I use it is because non webmail clients are becoming harder and harder to find and this one also supports Gmail, iCloud, and most important to me IMAP

The Journey begins

The problem of inverse images has existed in mailspring for a while, and there is no easy solution for this, and the “fix” I implemented is not a solution by any stretch of the imagination, it is a bandaid

The first thing I did was look at how the them did its thing, I was hoping it was a sensible method of doing style replacement, or a clever method of doing the same thing, instead if like all darkmode in Mailspring was doing inverse(100%) on email content this is not good, because it means every element is inversed and I had to re-inverse or stop the inversion on images

So that was the intial tact find the “img” tags and stop the inversion, this worked and was a lot easier than I thought, horray, so clicked through some emails and everything seemed fine, that was until I got to an email that was using “background-image” and now the problem exited again, damn it

I wasn’t the first to notice that background image inversion was nasty, it was spotted reported in 2018 and in 2021 it was moved to the forum, so this bug has existed for a while

Luckly because Mailspring supports themes and plugins and is written in electron, I can hijack the element and inject some JS into it, so I did it with brute force and got it working

export default class BackgroundImageFix extends MessageViewExtension {
  static renderedMessageBodyIntoDocument({document, message, iframe}) {
    const frameDocument = iframe.contentWindow.document;

    const tags = frameDocument.querySelectorAll("*");
    tags.forEach(tag => {
      let fixInvert = false;

      if (getComputedStyle(tag).backgroundImage !== 'none') {
        fixInvert = true;
      if (tag.tagName === "IMG") {
        fixInvert = true;

      // using this method so more can be added later
      if (fixInvert) {
        tag.style.filter = "invert(1)";
        tag.style.color = "#000";


Now this method is not good, its very system intensive, but it works, and it gets destroyed and re-initiated on each mail opened, which is the nature of the plugins in mailspring

But it works, and is now part of the Dracula official theme for Mailspring

Series: none