The three colors are the right balance in my opinion. Just one more or less would screw it up. As it stands the messages they each convey are very clear:

Green: You have less than half the level of hate the tank has.
Yellow: You have more than half the level of hate the tank has.
Red: You have almost as much hate as the tank and need to slow down.
Blinking Red: You're the tank!

The numerical layout for incorporating orange threw the significance of the 50% milestone out the window, which already makes it undesirable. If you were to preserve the halfway milestone, then orange would lead to a convoluted mess of colors above halfway. Putting extra colors below the halfway milestone is pointless because you never need to know how little hate you have. If you're green, you're green. Whether it's 20% or 50% is irrelevant, it doesnt matter since you're safe and not in danger of taking hate.