You can use Maya’s 3D Paint Tool to initially sketch out (“lipstick”) where paint should be applied to an object. Painters can then paint more strategically in Adobe Photoshop because they can easily see where to apply the paint. This works especially well for models with UVs that don’t give you enough information to paint effectively.
You can also start by mapping file textures (rather than using the 3D Paint Tool).
To lipstick a model
The painted textures are inserted as the base layer in each layer set.