No, and assuming so has cost plenty of owners an unnecessary repair.
Cold vapour is normal on start-up and clears as the engine warms. Unburned fuel from low compression, a cold cylinder or an injector fault also shows white or grey and usually comes with poor running. Steam from water entering the combustion space or the exhaust looks similar again — but on a wet-exhaust marine engine, ordinary cooling water leaving the exhaust produces visible vapour on a cool day with nothing wrong at all.
Read the context. Does it clear once warm, or continue? Is coolant level falling? Is there oil in the coolant or coolant in the oil? Does the engine run roughly, and on all cylinders? Is the smoke worse under load? Does the header tank pressurise or blow back?
Those answers separate a cheap fix from an expensive one long before anything is dismantled. If coolant is genuinely being lost with no external leak, that is the point to bring in a technician for proper testing.