Pull upper radiator hose off thermostat neck. Pull lower radiator hose off water pump. Take a garden hose on high and blast it through each radiator hose and by the cap, etc. Jam the garden hose on high into the lower part of the water pump. Take the coolant resevoir off and clean it very good. Now put everything back on (hoses, resevoir, etc.) Mix yourself at 60/40 mix (water-60, coolant-40). Fill the radiator up about an inch before the top. Put some in the resevoir to the cold line. Start the car with the radiator cap off and the heat on HIGH. Burp the system a few times by letting the thermostat open and close while you fill it up a tad. Air will escape this way.
It really depends on where you live. If you live in an extremely cold climate, then run 70 antifreeze/30water, or really hot = 30 antifreeze/70water.
The reason the coolant appears to be orange is because the radiator and the block have some rust. This is normal. Iron + Oxygen = rust. But you should flush the system like stated above. That should remove the rust.
If you are really lazy (or don't want to unplug the radiator hoses and make a mess in your garage/street), you could unscrew the drain plug on the radiator, let it drain, put the plug back in & fill it back up with water only. Drive it till the engine is hot, drain, then refill w/ water. Repeat the process until the water drains perfectly clear. Then add your custom mix of antifreeze/water and you are set.
Autozone sells some radiator flush stuff too. Just depends on how you want to tackle the operation.
Scott
Be carefull if you put any radiator flush chemicals in your radiator. I did it in a '67 and it cleaned everything out, including all of the rust that was plugging about a dozen pinhole leaks on the radiator.
Just run a bunch of water through it.
The real reason for the rust is water + heat +iron + aluminum. That creates a battery with coolant electrolyte. There is no good way to stop it, but you can slow it down with iron heads, iron intake, iron timing chain cover and a copper radiator.