The "Jedi" part of the Warlock is using the blade pact stuff for light sabers - conjuring a mysterious weapon out of thin air and wearing light armor or robes. And then the spells can be used primarily for telepathy/mind powers. Detect thoughts, clairvoyance, telekinesis, etc aren't inherently "dark" powers. Create Thrall, maybe, but even Obi Wan used mind tricks all the time.