Hello,
the command 'show interfaces x' should tell you which MAC address the port channel interface is using (which indeed is the one of the first port channel member interface):
S1#sh int gigabitEthernet 0/0
GigabitEthernet0/0 is up, line protocol is up (connected)
Hardware is iGbE, address is 52de.5467.9c00 (bia 52de.5467.9c00)
S1#sh int port-channel 1
Port-channel1 is up, line protocol is up (connected)
Hardware is EtherChannel, address is 52de.5467.9c00 (bia 52de.5467.9c00)