Strange but true, 305 V-6 valve covers on 1963 GMC 1/2 ton pickups came with a red, yellow, and black plaid design. The red color was used on the remainder of the engine without the yellow and black markings.
These photos are of an original untouched V-6 GMC engine. At this time, we are unsure why GMC used this appearance. (Maybe Scottish plaid implied good fuel economy.) Whatever the reason, it will be almost impossible for most perfectionists to restore a pair of the valve covers with the correct plaid appearance!