The game decides when it updates, if it does at all, blip colors. The code explicitly sets the color for it in all cases but the game doesn't necessarily visually update it.
MaxCarCrews directly controls how many are allowed to exist in the world so lowering the value should decrease the occurence because it will be creating less per tick since it will reach the max sooner in most cases. The max crews are determined by 2 factors. If the total amount of crew cars < than that value it will create more if it can until it reaches, or, it will do the same if the amount of crew members is MaxCarCrews * 4 to approximate a situation where every car (doesn't happen, but is a decent way to do it) might have a driver and 3 members inside.