The alternator cover is number 2 shown in the diagram and comes in black.
This item fits the following models: Triumph Liquid Cooled Bonneville T120 > AC6129, Bonneville T120 Black > AD0138, Bonneville T100 > AC5926, Bonneville T100 Black, Bonneville T120 Black AD0139 >, Bonneville T100 AC5927 >, Bonneville Bobber > AC1195, Bonneville Bobber Black, Bonneville Bobber - AC1196 >, Bonneville Speedmaster > AC1200, Bonneville Speedmaster AC1201 >, Speed Twin, Street Cup, Street Scrambler > AB9836, Street Scrambler AB9837 >, Scrambler 900, Street Twin > AB9714, Street Twin AB9715 >, Speed Twin 900, Liquid Cooled Thruxton and Thruxton R.