Pokemon cards with red HP are older cards, such as the 1st edition base set Charizard.
All the other 1st edition base set cards that I've seen have red HP as well.
Base Set is also unique in that Wizards were still experimenting with the layout and aesthetics of the cards after the 1st Edition run, which becomes apparent when cards from both 1st Edition and Unlimited are compared. The most obvious change is the weighting of text for HP values and attacks; they are much bolder in Unlimited.
Cards from the Evolutions expansion don't have red HP.
Source