Which Coolant?

OK! Probably was viewed so many times but I'm just curious and need a 100% accurate answer. Which coolant do I use in my Aluminum headed/Aluminum Radiator 340? Seems like there's a red coolant in there now but it's due for a change plus I'm replacing my water pump and hoses. I want to make sure that it's good for the block and the Aluminum heads/Radiator. I plan on flushing as much of the old stuff as I can. Thank you!