Thank you.
I’ve opened a PR here https://github.com/Foundry376/Mailspring/pull/2395
I think it would especially benefit from someone else testing it, as I don’t have a testing setup for all the Linux desktop environments
For now, I am replacing the white icons with inverted ones following instructions from Reddit user void_matrix found here: https://www.reddit.com/r/linux4noobs/comments/1f9zkdz/how_to_change_the_mailspring_notification_icon_in/
In may case, it was in /usr/share/mailspring/resources/app.asar/internal_packages/system-tray/assets/linux/
I made a script to automate the whole thing, requires npm and imagemagick to be installed
#!/bin/bash
if type npm convert &> /dev/null; then
sudo npm install -g asar
sudo cp /usr/share/mailspring/resources/app.asar /tmp/
sudo cp -R /usr/share/mailspring/resources/app.asar.unpacked /tmp/
sudo chmod 777 /tmp/app.asar
sudo chmod -R 777 /tmp/app.asar.unpacked
asar extract /tmp/app.asar /tmp/mailspring
convert -negate /tmp/mailspring/internal_packages/system-tray/assets/linux/MenuItem-Inbox-Full.png /tmp/mailspring/internal_packages/system-tray/assets/linux/MenuItem-Inbox-Full.png
convert -negate /tmp/mailspring/internal_packages/system-tray/assets/linux/MenuItem-Inbox-Zero.png /tmp/mailspring/internal_packages/system-tray/assets/linux/MenuItem-Inbox-Zero.png
sudo rm /tmp/app.asar
asar pack /tmp/mailspring /tmp/app.asar
sudo cp /tmp/app.asar /usr/share/mailspring/resources/
else
echo "This script requires the following packages to run: npm imagemagick"
type npm &> /dev/null || packages+="npm "
type convert &> /dev/null || packages+="imagemagick "
echo "Missing: $packages"
fi
5 years later and dark tray icon beyond our reach?
Hey folks! Mailspring 1.17.4 was released this morning and adds dark/light system tray icon support on Linux (#2602), which automatically adapts the tray icon to match your desktop theme. After many years I think we finally got this sorted 
Please update to 1.17.4 and let us know if the icon now displays correctly on your light-themed desktops. I’d love a few more eyes on this change, because on some distros (eg: Ubuntu), the system tray remains dark in the light theme by default. I’ve verified that case is handled correctly, but we may need to make a few distro-specific tweaks.
I just updated, I’m using Ubuntu 22.04, and the new icons are not working correctly. I suspect that symbolic SVGs might not been used. And they hardcoded the icon that should be used, creating the problem.
Ahh wow interesting, I looked at Ubuntu 25 but not Ubuntu 22, surprised that they’re behaving differently. Thanks for the quick reply, I’ll get this resolved in the next patch release. I think you’re right that we need to use symbolic SVGs and not try to provide the correct color (black / white) icon to really do this for platforms where the system theme does not change the color of the status bar.
I second that: on Linux Mint 22 Cinnamon with dark panel, the icon is now dark and not visible. It worked for me correctly in previous versions (the icon used to be white):
Hey folks - Version 1.18.0 shipped this morning and includes another fix for this. On GNOME/Unity desktops, the app will use the white icon variant, since the bar has a dark background regardless of your system theme (#2610). Sadly it seems like Electron is a bit behind and we can’t use symbolic SVGs / template images on Linux, so we’re stuck using a bunch of logic to determine the correct icon color. If this doesn’t resolve the issue for enough people, we have to go the path a few other apps have and allow you to configure this in the app’s settings.
If you’ve been affected by this, please give 1.18.0 a try — update via snap refresh mailspring, the built-in auto-updater, or from https://www.getmailspring.com/download.
Thank you for the quick turnaround!
On Linux Mint 22 Cinnamon (with Mailspring installed through a .deb package, as Linux Mint discourages using snap) the update did not help - the icon remains dark on dark background.
I am completely fine with configuring it manually, although I wonder whether there could be a way to return to the way it worked before when the icon was visible with no issues.
I confirm that everything new dark/light tray icon works flawlessly with KDE too.
The last update solves it for me (I set the icon to “light” manually). Thank you!