Draw Mesh Renderers and Terrains in different colors to show their StaticEditorFlags.ContributeGI / ReceiveGI properties. With default colors:
Yellow means 'ContributeGI' is off.
Blue means that 'ContributeGI' is on and the object receives GI from lightmaps. Additional resources: ReceiveGI.Lightmaps
Red means that 'ContributeGI' is on, but that the object receives GI from Light Probes instead. Additional resources: ReceiveGI.LightProbes.
All colors can be adjusted under Preferences > Colors.