Baldur's Gate : The Sword Coast Chronicles : NWN2 Persistent World

Perhaps at Level 1, Grant the Warlock a Free Feat from a List of Pacts, which if anything are just cosmetic in appearance for effects such as Hideous Blow or Eldritch Blast.

Dark Pact: Deep Purple
Fey Pact: Light Green
Infernal Pact: Red
Star Pact: Black

Sounds good.

From there, we might even be able to start to build Invocations that can be Pact Specific? Like a Word of Change (Fae Pact) Which isntead of turning you Horned Devil, Perhaps a Fae of some sort?