^^ Although you are correct, its also important to HAVE YOUR CAR with you when you get paint. There are often alot of variances in colors so they can find the RIGHT one for your car. I'v seen it plenty of times where 1 paint code matches ~8 paint chips.
At the factory, they dont really care what EXACT color the car is painted, as long as its all the same color. Its often off by just that little bit, but thats enough to have panel painted parts to look way off whack.
As I probably stated in the thread jepherz posted, and want fix it PROPERLY I would use a fusor product.
You can use a normal "bondo" but I highly discourage it. Plastic and mud expand differently from heat, so it WILL fail eventually..but if you want to use a rattle can paint, I doubt you are too concerned.
Just be advised, it WILL NOT look good with rattle can. A bumper can be painted for under $100 in materials easily.