Toby, that depends, to some extent, on whether you are referring to white gold or platinum. To the untrained eye, the two may look similar, but they are different and must be cared for differently.
Platinum is one of the strongest and most enduring of all metals, it is also one of the heaviest. The production of platinum requires very complex processing techniques that were not available until the end of the 19th century. Moreover, the high melting points of platinum made it very difficult to work with it. It was only with the development of new refining techniques that platinum was made more widely available.
To create white gold, yellow gold is alloyed with other metals, and therefore the gold will always keep the yellowish shade. To give it the “white” look it is dipped in a rhodium liquid chamber that covers it with a white rhodium coat.
In general, however, you can care for white gold and platinum in the same way you would care for normative yellow gold. Grease can be removed with rubbing alcohol, but I would recomend a commercial cleaners and the soft chamois cloth found in hardware stores.
For certain gold jewelry, an ‘ultrasonic’ cleaning machine, available in retail stores, may be appropriate