Anti Freeze turned brown.

I think you should be ok. Some of the things said here are the extreme. I only change them at work if they are leaking.

Mine are honestly not leaking, And the car runs very cool with the temp right on mark at 180 degrees.
I may try taking out that block plug near the oil filter, and drain the block. And of course, flush the system, with chemical, with the thermostat out. Eventually it should clean itself out with driving, and flushing.