Well "rhodiage" is rhodium plating, which is done to delay the process of tarnishing, but judging by the fact it's a list of défauts, I can't help but think that what they mean is that the rhodium plating is wearing off (they put it on deliberately, but later it can wear away). So I can't help but think they mean rhodium wear here.

The cheap nickel will give a pale yellow 'white' gold mixture, paladium will
give a pale white 'white' gold mixture, very near to the unpolished
platinum equivalent.

Now both these 18ct white gold mixtures (alloys) will need to be rhodiated
or rhodium plated.

When the rhodium plating, in time, is worn away the cheaper nickel alloy
variety will show a pale yellow shaded area coming through, the paladium
mixture (alloy) will not but will only show a more mat or unpolished surface
hardly noticeable against the already worn and tarnished shiny rhodium surface.

In time the rhodium plating will wear away, this will depend on the quality of the plating itself, if poorly plated then within 6 months signs of wear will appear, however, if properly plated it will certainly last at least 3 years, in fact just as long as would platinum, which, as with rhodium, will have lost most of its 'shine' and will need to be re-polished as well.
http://www.jewellerywebshop.co.uk/platinum_gold_rings.htm

"My fiance bought me a white gold diamond engagement ring from the jewelers and placed it on my finger 4 days ago. I used a Chlorhexidine alcohol handwash and within minutes the white gold started to turn yellowish. I was very upset because i have been reading other people's accounts of their own rings and they have been fine for at least a couple of months before the Rhodium plating was worn away. Is it possible to get it back to normal with replating? What should I do?
Thank you for your time."
http://experts.about.com/q/Jewelry-Gems-Minerals-689/Rhodium...

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Note added at 1 hr (2006-07-26 13:42:55 GMT)
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A couple of examples (albeit relating to other items of jewellery):

"The earrings are in excellent mint condition with no wear. No missing rhinestones, no enamel wear and no silver rhodium wear."
http://www.trocadero.com/moradaridge/items/516677/item516677...

"The brooch... is in excellent condition, very clean and has only minor rhodium wear on the back from handling."
http://www.cyberattic.com/stores/moradaridge/items/429053/it...