The Black Rats
The parade colors of the Federated Commonwealth Corps are navy blue with gold banding on the arms and legs. Gold is also used on the upper torso of the 'Mechs and the turrets of armor units to highlight panels, resulting in a checkerboard pattern. Other units have taken a perverse pleasure in infiltrating the RCT's facilities and painting a yellow streak down the spine of each 'Mech or on the turrets of vehicles.
Per FM:Federated Suns, page 93.
The insignia of the Federated Commmonwealth RCTs is a hybrid of that used by the Federated Suns and Lyran Commonwealth; the backdrop is the Davion Sunburst, over which is the mailed fist of House Steiner, and in front that the Davion Sword. The regimental insignia depicts a black rat on a white disc.
Per FM:Federated Suns, pages 90 and 93.