you mean "flop", right?
make sure the car is clean and if the paint is oxidized to then compound the area you are color matching. It helps to have an extra set of eyes to compare opinions with as well. Each person's eyes are unique in that certain people pick up certain colors more than others. You might see something that seems a little "blue" to be a match but someone else might see something else, so don't be afraid to ask multiple people what they think and try to avoid deciding too quickly. When you see the chip you'll know right away but just make sure.