Dont paint flag on your car.just paste flags if u want.
If u r desperate and really want to paint flag on your car thn you should
1-cover the place with white papertape.(u have to done it accurately so tht no space is left)
2-take water colours and paint flag
3-if u want to remove,just remove the tapes.
But boy if u gonna make urself then i must tell u its very hard. Flagging my corolla hood took too much tym and effort.....wooooo
but if can pay labour then its 8k for whole car.Rst is ur chioce