Anti Freeze turned brown.

Seriously doubt you have a blown head gasket. It will more than likely take a lot more than a little bit of water form a garden hose to get rid of the rust. Should have kept the old stuff on it and flushed it with some chemicals before replacing everything. Someone on here was talking about using CLR as a flush, never tried it but it might work. What you might want to do is hunt down one of the filters that goes into the upper hose and flush it with an acid based cleaner. My Fairlane has one of those filters, will let you know what it is....Did not have to go look....Coolant Filter that goes into the upper hose. Motor in the Fairlane is very rusty so I put one of these in it as a band aid fix so I could drive it for a while.