Blue is a safe option, (Halfords 2 year, Bluecol, Bluestar) most others are 5 year organic which you dont want to mix with anything else.
Drain and flush several times with Speedflush or similar to really clear it out before finally filling.
You'll only get about half of it out via the radiator tap unless you get under and remove the screw in plugs (knock sensor) but I wouldnt risk that, so lots of flushing and running is a simpler option.
Give thought to disposing of your old coolant as its attractive but lethal to animals..
Dont put it into drains as it'll end up in rivers etc and not down the toilet either as that ends up somewhere else.
I dump mine in the old oil tank at my local recycling centre.