In real life, vehicle ownership & usage can change frequently, and it can often take time for the current operator's livery to be applied to all vehicles (if at all).
The majority of Ready-To-Run scale model vehicles are reproduced in the colour scheme & branding of the organisation which operated the vehicle.
Categorisation can be a challenging (and often contentious!) topic. Some definitions which help us:
A lot of kit models are supplied undecorated.