I don’t know if this has been mentioned before but there seems to be a bug when trying to change layers’ colours from object property’s palette. Steps to duplicate the bug.
Select an object in the viewport
Open object property’s palette
Click on the colour box next to Display Color: By layer and try to modify the colour
You cannot change the layer color from here. You can change the object color by changing the Display Color field to “custom”, and then click the color box.
I don’t have access to a Windows machine right now but I’m almost sure that you can do that in Rhino for Windows, in fact it’s a pretty handy feature when you have a file with many layers.