Just flush the system out and use whatever you want!

Ive never heard of antifreeze gelling up - i think thats a scarestory!!

Generally Blue is ethelene glycol and Red is OAT (organic antifreeze technology)
If you mix the two - they cancel each other out!!

Some red antifreeze is methanol - very cheap but pretty crap.
Not many places stock this stuff now as it only has a 1 year life.