For incoming MPLS traffic, the traffic class/color combination is set according to the EXP bits in the outermost label, either per the policy attached to the label or per the per-VR rules. The policy has precedence over the per-VR rules. Therefore, fabric queuing is always based on the outer label's EXP bits.
If the traffic is label-switched through the router, the EXP bits value associated with the incoming label that is used for switching—which can be either an outermost label or an inner label after popping one or more outer labels—is passed onto the egress line module. This behavior enables the EXP bits value to be copied to outgoing labels, used to reset the traffic class/color combination on the egress module, or both.