Like squeeze said there is no reason to mask for your first color just make sure you apply enough paint at least 4 " past your breakup line this makes sure you have good coverage at the break, also if your going to use any metallic paint apply some color blender clear on top so if there is some bleeding from the other color you can simply clean it off with some pre cleaner, I'd also recommend using 3m's blue 1/4 " plastic tape for your breakup line its a little pricey but worth it.
Good Luck