Were it me, I would pick up a gallon from the dealer if you are just looking to top off. That way, you won't end up with an awful looking mess when you mix different colors even though they claim to be mixable.
I plan to do this for my wifes 05.
When/if you finally do decide to flush and/or change it, take a look at the Prestone Global GO5 amber coolant. I just did a complete flush/refill with this on my 01 Durango, and so far am very pleased. The D came with the factory green stuff that only lasts for 3/30, so I was not going to continue that way.
05 Linen Gold Pearl Dodge Grand Caravan SXT 3.8L (hers)
04 Flame Red Hemi 5.7L Dodge Durango SLT