Simulate Air Flow


I’m trying to simulate an air flow that changes its color from red (hot) to blue (cold). Currently i’m thinking about arrows that travel on invisible conveyors.

I want to change the color of passing arrows with a sensor, that detects the part and changes it’s material, if possible fluently and not in an instant.

In my first tries the arrows do change to blue, but instantly sadly.

Does anyone have some ideas how to solve this? I’m completely open to other ideas on simulating air flow.

Best regards and happy holidays!