The C&O took control of the B&O in the early 60's but the two roads operated more or less separately until the Chessie System was established. During the later part of the 60's the C&O and B&O started painting their E-8's in a simplified version of the C&O scheme. The only difference being the C&O or B&O letters on the side and the herald on the nose. As the repaints were done the C&O engines were renumbered into the B&O's passenger engine numbering system. There was some mixing of C&O and B&O E-8's as this point as I believe the number of C&O passenger trains shrunk faster than the B&O's freeing up the C&O engines for service elsewhere on the B&O.
C&O and B&O passenger cars started being painted in the C&O's tri-color scheme starting in the mid-60's except there was no roadname in the letterboard and either C&O or B&O heralds were placed at both ends of the car depending on which road's car it was. However, not all cars were repainted so trains of that era could have a mix of classic B&O blue and gray or C&O tri-color.
The MTH numbers for the tri-color cars are 30-67146, 30-67147, 30-6714, and 30-67149. But, it shouldn't be a problem to mix in some of the earlier B&O paint schemes into the consist.
Ken