I've been currently painting/building the 1/72 Airfix Spitfire Mk.1a for a while now, and here's where the daft question comes in...
Instead of painting it in the scheme that's on the box (P9495), I started painting it with a black and white underside (P9374), the main question is I've tried numerous different paint's now including the one from the 1/72 Airfix Hawk, and the Matt and Satin ones (on 3 different spitfires) and none of them seem to come out like the black does, also another daft question what would the best way be of getting a perfect straight line down the middle, I've tried various ways of masking tape but it always seems to encroach either the black or white area, I've added a photo so you can see what I mean:

Thanks in advance
John