Overheating with steam from inside of right cylinder head

My 1971 E-Type Series III V12 suddenly overheated. I’d had no prior problems. There is some intermittent faint white steam or smoke coming from the valley side of the right cylinder head which is more noticeable when the engine is first turned off . A combustion chamber leak detection test resulted in the blue fluid turning green (not yellow as it should for a gas/petrol engine). The best information I can find says that when the fluid turns green rather than yellow it indicates a there is either a very minor combustion chamber leak or there is residual exhaust from an intermittent leak. The fans are operating correctly. The thermostats are new with the correct toggles. No other cooling system leaks can be found. My suspicion is that there is a head gasket leak at those head bolts on the valley side of the head. What are the opinions of those more experienced? Thank you in advance for you help!