fluid in overflow tank different from radiator green

[Joesprocket]

Hey everyone, quick question about coolant fluids.

I'm getting ready to replace my temp gauge sending unit and to do so I'll need to drain the coolant from the radiator petcock. The fluid in the radiator is fluorescent green however the fluid in the reserve tank is orange...like GM Dexcool orange. I've had the truck a little over a year and this is how it came. Anybody have a guess as to why the 2 different fluids? They should both be the same no?

I appreciate the help for the 'new guy'.