In terms of "styles" as in fashion or armor, Lancelot, like other knights of his era, would have been depicted in armor and clothing reflective of the medieval period. This includes plate armor, chain mail, and a coat of arms representing his family or his own heraldry. The specifics of his attire and armor would have varied over time and according to the artistic or literary source.
A long, structured coat in charcoal or navy provides the "cape" effect without looking like a costume. lancelot styles porm