Hello,
Can I use an RGB light sensor to detect a moving target (e.g., someone running) with a fluorescent color?
Best Regards 
Can you use a tire for your car?
It heavily depends on the type you use aka be more specific 
OK. I will give an example.
Let's say that the tires on your car are red. I have the sensor 1m away from the exit of a mechanics shop.
Assuming that no other car inside has anything red, can I detect that something red passed through the exit?
Best Regards!
Depends, what's your eye sight? Do you have you're glasses on? Are you actually looking? Is there any light at all (with the correct wave length)?
Aka, just give the damn type of sensor you want to use
The subject may be to far for the sensor to detect. You may consider adding optics to your project, depending of your skills and availability of certain optic items in your area.
The sensor can detect colors - in your case we are talking about changes in the position of colored spots that make up the subject. This is a coding task.
From my experience with color sensors, I can say that procuring a reliable and well-documented one is advisable. Or to check various brands/types.
I have the sensor 1m away from the exit
Is that a meter or a mile?