PID Controller for a simulation of a curtain coater speed for a certain code color

Hey, I am searching for a TinkerCAD (and Mathlab code for a curtain coater where we can control the conveyor belt speed depending on the color code (for color consistency) through a light sensor . So if we have a lighter color than the target, the conveyor belt will slow down in order to get into the target zone

The Mathlab code is needed for a mathematical model with boundary conditions (our target color codes, minimum and maximum speed)