PJ, I think you are right.
If it is poorer quality white gold or re cast 'old gold'. I say poorer quality white gold because the white gold is down to the alloys that are used to make the gold actually white. There is no such thing as white gold and can be less predictable than purer yellow gold. I am sure I read somewhere that is why more and more jewellers are using Palladium but it is more expensive. I also heard that white gold from America, Italy and India uses nickel to 'whiten' their gold because it inexpensive,bleaches the yellow gold easier and is a better colour match when mixed with 18k but less predictable when mixed to 9k, it can react more in casting, the colour match for 9k not as predicable. I also heard that an EU regulation using nickel in jewellry is being implemented because of nickels slightly carcinogenic worries.
Saying this , I love white gold and can by pass yellow gold especially the buttery 18k stuff.
I have a palladium ring that gets really bashed about and so far no hints of yellow coming through.
I suppose Platinium is the best and I am REALLY please to see a few pieces on Gems ( just saving up for a buy)
Maybe a 'gold expert' can confirm what I was told. I had a quick 'google' and seems I am on the right track?
Maybe Gems TV was having to much hassle with white, the casting, the quality(don't forget Gems Tv gold is hall marked in Birmingham , maybe their white wasn't testing so well to many other alloys within the gold? Maybe it is all down to money and GEMS thought they would sell the pieces in yellow anyway without the hassle?
I did have a white 9k ring from Gems that just blew up (due to all the air bubbles within the ring shank)