Making a game capture points like in bf3

I am making a fps game. I wanted to make the game have objective like in bf3. There is a circle whit changable color telling which team is holding it. if enemy enter, the circle turns red while team enter, it goes blue.i included a picture to see what exactly i want.Thaks.16160-flag.png

Use some image tricks and to help ya PRO Effects.
Also, you need to script, which player team is near the flag.
And make a load balance about conflict to attack/defense flag.