The Red LED will light up when VCore booster is pressed. When one Red LED is lit, VCore is boosted by +0.v. When 2 Red LEDs are lit, VCore is boosted by +0.2v. To stop the VCore boost, just press again and VCore will go down to what you have set. The 2 buttons are exactly the same in function each.
Vtt Booster
The far right button on the EVGA ECP increases the VTT voltage by +0.1v.