I was the FO. Captain called 'GO' just before 100kts when we got a BRAKES HOT Amber ECAM warning on one brake - only 300ish degrees. We decided to leave the gear down to cool it off and the Captain made a great call to the tower so everyone knew what was going on. Cooled it down, got them up, and off to wherever we were going. Probably a quick turnaround and the long taxi down to 15 put some heat into the brakes.