Layer's icons may have different colors, as e.g. in the “A4 leaflet 3-fold Roll” document template:
A layer's icon color is repeated in the status bar, too (near the layer's name):
But in the “Layers and Objects” dialog there is not an option for changing it, nor in the layer's context menu:
How to change it?
(Inkscape 1.2)
You can also click on the colored line to the right of the layer/object name in the list, which opens a color picker dialog.
It's a small target, so it might be easy to miss while trying to click on it.
Select the layer, and in the “Object Properties” dialog (Object → Object Properties...) you will see its color:
Double-click on it, and you may select your desired color.
