Reported in viewtopic.php?t=8136, but separated for the sake of visibility
[*]The expand/collapse arrow icon is set to 'white' with Dark-Mode enabled regardless of defined custom list appearance color. The arrow will be nearly visible when a light appearance color is chosen.
[*]The opposite can also happen in Light Mode. Choose: a black list appearance color and the arrow will "vanish"
Options:
* Manual control over the arrow color (maybe even define the arrow line yourself)
* Draw a border across the arrow in black. Will be invisible without custom list appearance color, and accentuate the arrow with some other color set. At least this appears to happen with the 'dotted' line which is visible regardless of the defined custom list appearance color.