Testing a headgasket leak on a cadillac northstar

This is a mac tools. Tester if the fluid turns yellow you have a combustion chamber leak. 2 min test with engine warmed up for 10minutes. Very handy tool

[@MrRahimhosein]

So its bubbling meaning there is a head gasket leak. But the blue fluid didnt change color, meaning that it is not leaking. What the hell?

[@Tom-wq2mz]

Blue it's Good. Yellow it's a blown Head gasket.