I am unsure what I would need to explain, so I shall give an example on how to do this.
Var [red] = [Sys/Clan/History:"HistoryName"]This should result in the effects being susceptible towards the history value of "HistoryName" for the Red value.
Fog [512,512]    [red,40,65]
//Remove Sys and/or Clan depending on which form of history you are using.
//Replace "HistoryName" with the name of the history value you want to have effecting the red color.