Also you are the one that chooses how far away should be displayed green and how close it shoud be changing to red. A simple way would be to place a dummy character on the baseplate then put a Part on the baseplate at the dummy’s feet. Change the length of the Part to what you figure the green should start changing to red, and at what point it should be completely red. Those will be your Magnitude distances in Studs.
What you could do is create tween. The tween goal is green when the magnitude is high, and red when it’s low (which means the character is near it)
Then, pause the tween if the character isn’t moving. (Humanoid.MoveDirection)
The issue with changing it only when the player moves is that if the object is moving as well you wouldn’t see it change.
Best to use a change of Magnitude, since that’s what the colour change is based on.