I would go for the white, personally. The ivory does look a bit too much against your skin, which is funny because for most of us it is the total opposite!
On the other hand, lighting in salons is AWFUL! I would ask if you could walk outside for just a minute (YES, they do this at some salons and give you a little hand mirror to take) and will go outside with you so you can see what the color *really* looks like.