How cultures are different across the globe, I would have used RED for hot, orange for heating and green for safe (instead of orange, purple and blue - love purple though!)
Interesting, I'm not sure that colorblindness can be severe enough for that to be a problem. I'm red/green colorblind, but I have no issue with stoplights or LEDs. Things onlystart to get hairy once the spectrum shifts closer to the browns such as forest green or burnished slate.