Why do some barbies have white printed panties?

It’s simply the design of the Barbie doll. Of course, the “B” is for Barbie. It’s just panties on the doll.

Because the Barbie’s amorphous, skin-colored, non-genital area is more disturbing to look at.

You mean that the doll is made with these panties printed on, or they’re a removable piece of clothing?
Ken dolls, when I was little, were made with tighty-whities molded onto their crotch areas, but they weren’t painted/printed – they were the same colour as his skin.

The premium Barbies come with the white printed panties, ie: the Happy Holiday ones etc. the more expensive ones…$30 and up usually.

I sense that another answer to this question could be found in this NSFW question.