Cycle Region in Editors - custom colour change not working

Preferences ->User Interface ->Custom Colours ->Editor Area Background ->Cycle Region

Setting a colour change here seems to have no effect…? Key Editor or Audio Editor.

Even tried to turn on Cycle mode - no colour change (except in ruler of course, under Ruler settings)

Am I doing something wrong…?

Same procedure but in the Project Area Background ->Cycle Region, changing the colour here, works.!

Anyone else.?