Vintage Barbie Fashion Pak Knit Slacks (1963)
Blue, Gold or Stripe Knit Slacks
The mustard gold slacks were also used in Knit Separates #1602 (1964). The pants have a snap closure in the back. I have seen the slacks less than the other items from this grouping, which leads me to believe that they are less plentiful than the other pieces, but still they are not terribly difficult to find.
This is part of the Knit Mix & Match Group Fashion Pak Group (1963)