The Assaultron is one of the few robots in the game that hasn't received an HD re-texture mod yet due to the complexity of the model, such as separate textures for each body part, as well all the tubing and machinery underneath the exterior armor plates.
This covers all Assaultrons, including P.A.M. It does not cover Assaultron Blades. In addition, this does not cover Automatron DLC paint jobs, just the standard Assaultrons.
Credits: fadingsignal