This Cities:Skylines mod allows warehouses, Processors and cargo trucks to be highlighted in the "Industry Areas" and "Natural Resources" view modes to more easily glean the flow of supply lines.
Warehouses for Goods produced by Player Industry processors (ie, Paper, Glass, Plastic, etc) are highlighted on the "Industry Areas" view when the appropriate tab is active (Forestry / Farming / Ore / Oil)
"Luxury Goods" warehouses are highlighted on all four "Industry Area" tabs.
Zoned Industry warehouses and processor buildings are highlighted in their resource color when the "Industry Areas" view is shown.
Warehouses for goods produced by Zoned Industry extractors (ie, Ore, Logs, Oil, Grain) are highlighted on the "Natural Resources" view in the same color as the four types of Natural Resources.
Finished goods produced by Zoned Industry (ie, "Commercial Goods") are highlighted on the "Natural Resources" View with the "Active" color.
Cargo trucks transporting Zoned Industry processed goods are highlighted on the Natural Resources view in the color of their respective resource.
In short, Warehouses, Extractors, Processors and Trucks are colored sensibly for the purpose of understanding goods flow.