Can I stifle the ability of Painter's Servant?

[Kerdo]

Can I stifle the ability of Painter's Servant?

[Twanos]

No, you can't.

Painter's Servant isn't an activated or triggered ability therefore stifle doesn't apply.

Painter's is technically a replacement effect, asking the owner to make a choice as it moves from the stack to the battlefield. Once it hits the battlefield the "chosen color" in the ability has been replaced with "red" or "white" etc.

[Kenji]

602.1. Activated abilities have a cost and an effect. They are written as "[Cost]: [Effect.] [Activation instructions (if any).]"

603.1. Triggered abilities have a trigger condition and an effect. They are written as "[Trigger condition], [effect]," and begin with the word "when," "whenever," or "at." They can also be expressed as "[When/Whenever/At] [trigger event], [effect]."

As Twanos pointed out, Painter's Servant doesn't have an activated or triggered ability, so Stifle cannot be used to stop any part of its ability.