Contrast paints, how do they even work?

I’ve been attempting to a Grey Death Legion lance following the camo spec tutorial on YouTube. In it, the author makes use of Basilicanum Grey contrast paint over a cool-grey base coat and dark stripes. In three attempts, I am always left with an ugly streaked brown that looks nothing like the product in the tutorial. Going on heavy with the contrast paint completely overwhelms the base coat leaving me with a mud brown color and going on light looks very streaky and very much still brownish. What am I missing? Is this a bad pot of paint or poor technique? General tips for painting with contrast paints would be very much appreciated as I’m very new to the painting hobby!