Better off leaving the pipe as is and just paint same color as wall. No material you put there in an attempt to trowel over the pipes will stick well.
The pipes only “stick out” to you. Almost all stuff like that sort of fades into the background, so to say. Pay real close attention the next time you walk down the street and deliberately seek out wires, pipes, etc. You might be surprised how much you never noticed or thought about before.
E.g. Are you inclined to cover up that downspout visible on the right?
There are 3 little outspouts protruding from the bottom of the terra cotta pot, I guess those are okay.
The watering system goes around both sides of the big blue intra-wall pot, are joined and then descend --I would be trying to make those more subtle, also.
But all these answers are really good and have me thinking more, now.
Ah! You're talking about the rain downspout from the roof, okay.
I see.
Somehow I'd never considered that, and that seems to bear out what you say, that cuz I installed the plastic painted pipes, I am tending to think about them very much.
Hmm...