Agree Oldfrog and it's not unusual for the coolant reservoir to be reddish/brown from rust from the engine anyhow. Believe I'd be flushing the whole cooling system, including back-flushing the heater core, and installing new coolant at a 50/50 mix with distilled water. Flush the heater core from the hoses towards the front of the engine and don't remove them from the core itself or you may damage the tubes.
If you want to see if oil is in your coolant before doing this buy some UV dye like below (not the AC UV dye type). Then add a small amount to your engine oil and let it run for a while until thermostat opens. Then use an ultraviolet light to inspect the coolant to see if the UV dye's in it. I bought a UV pen light with the yellow glasses kit at Autozone for $11. Looks like it's up to $16 now and they also sell the dye.
NAPA UV dye:
UV penlight/yellow glasses from Autozone:
UV dye from Autozone:
Often a an engine temp of 220-225 isn't enough to blow a head gasket. But this is the coolant temp where the heads may have become a whole lot hotter with the T-stat in backwards and no coolant flowing through the system. The miss at WOT may be a whole other problem but it's worth checking the coolant using UV dye. Good luck.