Hi Chung_Chiang. I did find your post while looking for a solution to pretty much the same idea you described. I am not sure you ever got a solution to your problem but was curious to know if you did.
I am at a forum called indesignsecrets.com/ where the community is pretty active and your experience would be very welcomed.
In case you have a chance, stop by https://indesignsecrets.com/topic/variable-colour-which-changes-from-page-to-page#post-996 13