How to turn subpixel antialiasing on in macOS 10.14?
Open the Terminal application
Type or paste

defaults write -g CGFontRenderingFontSmoothingDisabled -bool NO

Press ↩︎ (Enter)
Restart the computer




To return it back, do the same but instead type in the terminal

defaults write -g CGFontRenderingFontSmoothingDisabled -bool YES




Update on 2019.10.12: the solution works in macOS 10.15 too.



Update on 2019.12.24: you can turn subpixel antialiasing only in a specific application. To achieve it, do the same but instead type in the terminal

defaults write com.evernote.Evernote CGFontRenderingFontSmoothingDisabled -bool NO


where com.evernote.Evernote is the identifier of the application. See how to get it in this question. Then restart the application.

To revert it, type in the terminal

defaults delete com.evernote.Evernote CGFontRenderingFontSmoothingDisabled


You can even enable subpixel antialiasing everywhere and disable in a specific application (it's left as an exercise for the reader).