Ye, this seems to be a bug. But I just found a turn around. Copied all the Marketing Channel setting from dev report suite (setting this as template) to prod suite. This resolved my problem.
Anyways, thanks for helping me.
No offense! but isn't the correct answer to the question "How do I change the Marketing Channel Color (...)? should be below
Go to report suite > Marketing Channel > Marketing Channel Manager > Channel color (last column in your screenshot).
Click on each Color Box to select the desired color option (27 options) > select a different color for each marketing channel.
Don't forget to hit save to apply the selected colors.
I know due to bug it's not working currently but it should not change the answer of the question? Lmk
Could you pls tell me how to copy channel rule settings across report suites? I only find function to copy processing rule not marketing channel processing rule