'Sella' word denotes how the rice is treated. Here, it means parboiled (partially boiled). The yellow color, which it adapts, is because of this treated process. Sella is rice (of any variety, incl. Basmati) whose husk has removed by boiling/steaming the paddy without damaging the seed coat and nucellar tissue thereby retaining it's nutrients. The advantage of this rice is that on post cooking each grain separates out perfectly, is pleasant to look, has good aroma. Sella rice also called parboiled rice (steamed while the grain is in the husk, and then dried and milled).
The number '1121' specifically identifies the variety of a hybrid rice.
1121 White Sella Rice
12.0 To 12.5%