Layers have been long capable of VPFREEZE, which makes all of the contents of a layer frozen in a particular viewport. Layers are of course, also capable of controlling an objects color: as long as an object is color is BYLAYER, then the color of the layer controls the colour of the object.
Up to rather recently, there was no direct method to manage layer colour unique to each viewport. Now there is a very cool blending of both features: VP Color. With this feature, the color of layers can be set independently for every viewport. One possible use is having a key plan that can show the same content as your drawing, but with faded colors.
Layers that have overrides set in them display with a light blue background color, making them easy to identify. (FYI VP overrides can also be assigned to linetypes, lineweights, and plot styles; these would have blue highlighting in any overrides, too.)
This is what the layer palette looks like with color overrides: we see affected layers highlighted, and the overridden colors displayed in the VP color column. For simplicity of viewing, I placed the columns near one another.
To remove a VP override, right-click in the layer palette and select Remove Viewport Overrides for in the popup menu. AutoCAD offers options to remove overrides of selected layers, or overrides of properties, or even overrides for specific viewports, or removal of all overrides in all viewports.
Lots of choice, lots of power.
The best part of VP overrides is that there is no longer the need to copy objects to other layers so it can appear differently in every viewport!