In so much as humans have to purchase their ships and NPC's are issued their's. I'd concur like most employer's whom provides any and all equipment to do the job, fancy paint schemes are not in the budget. Though they may look cool, it is the belief of most companies that Chrome and or fancy paint schemes, don't pay the bills!
Updated with additional reason:
There are system in which the distance from the star to the destination is on occasion several million Light Seconds, which equates to a few LY's, one way. One can only imaging what the speed that an NPC can reach when go from or near ones destination to the star that they just left, wait until you get a few Ls from the destination and when slowing down to the '7's", interdict you; Which works out to be twice the distance you went. Though it may have taken you over an hour or more to get there, they can travel from and too in seconds. That kind of speed shreds paint.