Bad head gasket or what? on 2003 Mazda Tribute

Temp gauge was all the way on HOT,and the water pump was seized, but I was told the engine checked out OK. So the pump, theremostat and hoses were replaced. After drving around for 30 min or so the fans came on, but ran OK. I thought mabe the sensor is shot from all the heat the night before. After I got on the highway and hit 70 she started to overheat, backdown below 70 ran cool, but the fans never went off. I went back to the shop and now the test fluid goes from blue to yellow. I have been driving the car around town and highway for a week now. The fans come on and she gets hot at highway speeds, but no condensation out the exhaust, the oil is clean and coolant is not dropping. Any ideas. Thanks for your time.

Asked by for the 2003 Mazda Tribute
Chemicals dont lie... If it changed color then you got exhaust fumes entering the coolant. You may not be getting coolant out the tail pipe cause the hole is still to small for the coolant to overcome the exhaust pressure.