In my opinion : Altcoins become red because Btc is going up (not only Alts value in Btc but also Alt value in Usd). Btc is going up before a fork because people want to get free tokens from the fork.So they sell Alts for Btc temporarily. So if there is a slight chance of a new token that will be tradable just after the fork, then yes probably Alts will again temporarily become red again because of the fork.