Fill the chip a thin layer at a time with black fingernail polish, let each layer dry until it is COMPLETELY dry (6-8 hours is good), and then polish it out with Stewart-MacDonald fine polishing pads: http://www.stewmac.com/shop/Finishin...hing_Pads.html
Start at 3200 or 3600, then go finer grade by grade until you have gotten it as smooth as possible with the 12000 grit. Then I use the Swirl Remover: http://www.stewmac.com/shop/Finishin...Compounds.html
This has worked for me. Done properly, one cannot tell there was an nick.
Testors model paint is good if you just want the nicks filled and covered, but the paint is too soft to do any sanding or polishing. Been there, done that.