Masque works on Autobar but...

[adorabull]

It doesn't seem to work on my ElvUI or Blizz frames for some reason. No error message, just not skinning. :(

[StormFX]

Re ElvUI: It's actually up to the author of the add-on to provide support for Masque, as Masque is just an engine that other authors use to skin their own project. (Masque is basically an extended library)

Re Blizz Frames: Masque has never supported the default UI. Its description specifically states,

Masque is an add-on for World of Warcraft that provides a skinning engine for button-based add-ons.

Note the part in bold.

[adorabull]

Thanks, will ask ElvUI about supporting your addon! Appreciate the clarification :D