Use a radial pattern.
This is just a modification of the one in the drop-down Insert menu.
torus {10, 1 texture{ pigment {radial frequency 35
color_map { [0.0 color Black]
[0.25 color Black]
[0.25 color Yellow]
[0.75 color Yellow]
[0.75 color Black]
[1.0 color Black]
}
}
finish { diffuse 0.9 phong 1 }
} // end of texture
