Want to do a radiator flush.. What coolant should I use?

I've been meaning to do change my coolant since I got my truck about 6 months ago since I've no idea how long its been in there. I bounced around from thread to thread and couldn't find a definitive answer as to what to best/right coolant is. There's green in it currently, should I do a complete flush and put in toyota red? Or just put some standard green back in it..

 

What year is the truck? 2nd gens should only be factory Toyota cooliant pink.

Cooliant has changed over the years. There Use to be specific cooliant for certaint cars... Now there's universal cooliant for all cars at all sorts of colors. Who really f**ing knows the real science behind the cooliant????

 

Use Toyota's after a good flush.