The IsoSurface itself can't be textured. The resulting TriangleMesh technically can. But since the IsoSurface can produce incredibly complex (and often concave) meshes, practically this would only make sense using 3D textures or using a (manually generated) UV map. For the latter you'd need to use an external tool to flatten/unwrap the mesh first. As an alternative and if you can classify/consider your result mesh as a more simple object (e.g. box or sphere), it's relatively trivial to compute texture coordinate for that proxy form. For example this sketch below produces spherical texture coordinates for a voxel mesh:
Even though it's not perfectly round any more, the general form still is sphere-like and so computing spherical texture mapping still makes sense. For something like
Dominik's meshes below it wouldn't...
