Actually the karatage does make a difference.
Basically, gold is yellow- 14karat gold is 57% gold, and 43% alloy. 18karat is 75% gold and 25% alloy.
Therefore it's actually easier to mask gold's color in 14karat- simply because there is less gold in it.
There's a huge difference in how the gold is alloyed.
I have found that some yellow gold looks yellower than others.
Some pink gold has more rosiness to it than others- this having to do with the actual makeup of the alloy- also the jewelry work, and polishing .
18karat white gold does require the best of both to get solid results.
But there are some people that have reaction to gold, no matter how well it's done- for example, Mrs Mitchell
We had a bad experience making a large man's ring ( for me) in 18karat white gold.
The properties of the gold were such that the broad surfaces had unrepairable porosity.
Porosity is tiny holes in the gold.
It can happen to any cast metal. Better casters have a low incidence. Better factories will scrap a gold part if it has a lot of porosity- small patches can be repaired using a laser.
Basically, not all 14 or 18karat gold is equal- but if you want white, I'd generally suggest going with 14kt, unless it's a high quality piece.
We've made quite a few pieces in both 14 and 18 karat white gold and other than the ill fated 6ct light yellow radiant monstrosity made for me, we've had no problems with yellowing of the white gold.
No question I'd be really peeved if someone told me I needed to spend $65 every three months to have a nice looking piece of jewelry.