My entirely uneducated guess is that a layer of paint would impede the cooling of electronics that depend on the housing to dissipate heat.Paint would also absorb more solar heat than plain metal.
I suspect there's a lot of re-thinking of how to land on a comet going on as well.
I can imagine a cage-like outer shell where the robot inside is able to rotate on two axes under power. Let it tumble any which way and then use sensors to determine the correct orientation and right itself.
NASA has a concept for this: https://ti.arc.nasa.gov/tech/asr/intelligent-robotics/tenseg...
I've tried to find a video showing it happening, but while there's lots of animations of bouncing, rolling, and the final opening up, they all miss the critical moment. Also, car safety videos are really badly poisoning the search results...
Here you go. Really enjoyed watching that.