In 3D Paint Tool Settings, the File Textures section shows a list of paintable attributes for the current texture:
If you want to paint attributes not shown in the list, such as Eccentricity for the Blinn material, you can first paint on a single channel (grayscale) attribute that is in the list, and then use Hypershade to connect the texture to the shader attribute not in the list. For more information, see File Textures section in 3D Paint Tool settings.
