You can use any Photoshop painting tools to paint directly on a 3D model just as you would on a 2D layer. Use selection tools to target specific model areas or let Photoshop identify and highlight paintable areas. 3D menu commands let you clear away areas of a model to access interior or hidden portions for painting.
When painting directly on the model, you can choose which underlying texture map to apply paint to. Typically paint is applied to the diffuse texture map, which gives a model material its color properties. You can also paint on other texture maps, such as the bump map or opacity map. If you paint on an area of the model that lacks the type of texture map you’re painting on, a texture map is automatically created.