You'll find so many plug-ins for painting in Adobe Photoshop out there. But the famous ones are: Color Constructor, Prisma Palette, Perspective Tools, and so on.
You can also check out various brushes by other people made specifically adjusted for painting certain parts such as buildings, hair, skin or editing. Keep in mind that you may encounter some brushes which needs to be bought in order to use them, but there's lots of free ones over the internet.