Change colour of locked pane title?

When I lock a pane, the colour of the title changes from pale blue to pale red (as opposed to just showing a lock icon like on the Mac version). I prefer everything monochrome, but I can’t find an entry for this in the Appearance settings – is there any way to change it?

The lock pane title color is one of the few colors not even Theme-builders can change in the QSS Stylesheet.

Probably because the bar is color coded programmatically.