Prestone Extended Life Antifreeze/Coolant is compatible with ANY antifreeze/ coolant – regardless of color – for use in ALL makes and models of cars and light duty trucks. This patented formula provides a high degree of performance durability and carefully balanced protection against temperature extremes and rust corrosion of all cooling system metals, including aluminum.
...from the Prestone website:
You'll probably need this (with instructions) to flush the old coolant:
http://www.prestone.com/products/print/461?popup=1
But yes, don't worry about getting them mixed a bit.
If you just drained and filled, you might want to do it again in the Spring or sooner. More of the old stuff should come out at that time.