Coolant Leaking From Wastegate?

Was the blue smoke when the motor was first started?  Usually blue smoke is oil, which can happen at first startup after the engine has been sitting due to oil leaking back into the turbo. Coolant typically makes white smoke when it’s mixed in the combustion chamber and it has a sweet smell.

If we start with the premise that the yellow stain is not associated with the blue smoke, then I would ask if wastegate shaft was lubricated at the 25 hour service.  If so, maybe the wrong lubricant was used and it had too low of temperature rating and turned that color with the exhaust heat.  

In the unlikely event this is a coolant stain, the only way coolant could get into the combustion chamber would be a cracked head.  Since the cylinders and block are not liquid cooled, there is no coolant that passes through a head gasket like in a car engine. So a head gasket leak would not allow coolant into the cylinder. If you suspect this, you should be loosing coolant. If you are, you can do a hydrocarbon test of the coolant to see if exhaust gasses are present in the coolant system.