If they are villainous and end up fighting another bad guy, the chances that they are A Lighter Shade of Black in that situation are extremely high. This character very rarely is a total villain, but also only rarely The Hero. More likely, they can be anything from a Knight in Sour Armor to a Noble Demon. While that can take a variety of forms, they rarely are the Knight in Shining Armor.
This places them rather high among the list of potential candidates for Dark Is Not Evil, or at least a sympathetic form of villainy. Note that, although being a black knight, this character is still a knight.
