3 a of the roller and are preferably undercut grooves in this regard each groove 15 17 has a longitudinally extending top slit 19 21 in communication with a laterally larger interior top pocket 19 a 21 a the top pocket 19 a 21 a of each groove 15 17 can hold an elongate longitudinally extending top attachment member 23 25 so that the top attachment members cannot fall out through the top slits 19 21 while the shade material 5 attached to the top attachment members extends downwards from the grooves the shade material 5 includes a vertically extending front layer 27 and a vertically extending rear layer 29 when the shade material 5 is assembled to the roller 3 the front layer 27 extends downwardly from the slit 19 of the front groove 15 and the rear layer 29 extends downwardly from the slit 21 of the rear groove 17 the front layer 27 has a plurality of elongate longitudinally extending parallel rectangular stripes 31 33 relatively opaque stripes 31 alternate with relative translucent stripes 33 the rear layer 29 also has a plurality of elongate longitudinally extending parallel rectangular stripes 35 37 which are alternating relatively opaque stripes 35 and relatively translucent stripes 37 the rear layer 29 can be moved vertically relative to the front layer 27 so that the opaque stripes 31 35 of both layers can be aligned with each other or with the.