Can't answer about the "proper" paint color for a Perkins, but most that I've seen are indeed blue.
Really recommend you rethink your desire to use brush-on paint. Spray paint is widely available, and is much easier to use and generally with better results. You can protect from overspray problems easily by doing a good job of masking. Draping plastic garbage bags is a good way to cover large areas. Use paper and tape for smaller spots.
As is all paint jobs, prep is key -- do the best you can to thoroughly clean and degrease the engine before you paint.