Ladder logic is a drawing of a relay panel that happens to execute. Two vertical rails carry power; every rung between them reads left to right as a condition chain ending in a coil. The editor that ships with a controller — RSLogix on the Rockwell side, LAD in TIA Portal — puts that diagram on a white canvas inside grey Windows chrome and lights the conducting path green when the rung goes true.

That green is not decoration. It is the diagnostic language a maintenance technician troubleshoots by at 3 a.m. with the line down. This system keeps the canvas white, the rails black, the mnemonics navy, and the chrome the exact 3D-face greys of the era — because that is what the artefact looks like.