It exists as an option in the layers dialog, but a button would be nice to to quickly access this feature. By default, it ought to be in the layers toolbar, but you could move it to the styles toolbar (which seems like a more appropriate place IMO) if you use it regularly.
- create a style with the color by layer option activated (is saved with a style)
- create a scene in your template file which only saves the style
- You can use this scene for a fast switch of the style to the one with the color by layer option
There is a free plugin toolbar with a button for “colour by layer” I use it everyday it comes with other very useful view toggle options for Guides / Hidden Geometry / Camera perspective-parralel view and more. It is called Custom Toolbars the author is Jim. You can get it through the Sketchucation Forum’s download section. Also try the “toggle units” (author is Matt666) plug-in it’s very useful