A few users have discovered that Mojave’s Dark Mode can have weird effects on various apps and tools, making pre-existing or sometimes new text content apparently vanish. Look really closely and you can see that it’s rendered in black on very dark grey.
A good example, kindly drawn to my attention by Stephan, are old Secure Notes viewed in Keychain Access. Although new notes shouldn’t suffer from this, many users with notes that were created in High Sierra and earlier are discovering that they can’t read them when in Mojave’s Dark Mode.
Help is at hand, in my free app DelightEd, from Downloads above. If you’ve got any styled or Rich Text which is playing up in Dark Mode, here’s how to fix it.
In the app which displays the text, select it all and copy it.
Open a new document window in DelightEd, and paste the text into that. It will still appear black on dark grey, until you use the Endarken command in the Edit menu to transform it into bimodal text. This is recognised by macOS as requiring display in black when in Light Mode, and in white when in Dark Mode.
If you don’t believe me, switch DelightEd’s window between modes by pressing ⌘3 for Light Mode and ⌘2 for Dark Mode.
Then select all that text, copy it, and paste it into your original Secure Note to replace its text.
You should now be able to read your note properly whether your Mac is in Light or Dark Mode. Save and rejoice.