On macOS the Arena 6.0.0 rev 60521 menus for Deck, Group, Layer, Column and Clip show a (partially) transparent background for the colour coding menu item. A screenshot of each menu with highlighting is attached.
To illustrate using the Deck menu:
Not sure if it matters for this defect, but I'm using macOS Sierra (10.12.6) on a MacBook Pro (model: Retina, 15-inch, Mid 2015) with discrete graphics card (AMD Radeon R9 M370X 2048 MB).