It is because it is almost not supported anymore. and is being faced out.
Before there was more of a difference between if an item was selected or checked.
It becomes more clear if you enabled "checkboxes" in settings so that it shows a checkbox in front of the items.
Before it was possible to have items that was checked and items that was selected and it did not need to be the same. But this has been removed (in most situations)
and it now keeps selected and checked synced. (The underlaying UI component still makes a distinction of selected and checked)
The "Selected" settings will be removed. (Or more correct, the "Checked" settings will be rename to "selected" and the one that is selected today will be removed)
So for now. use the same color for "selected" as for "normal".