Video: Contrasting-Color Cast-On with Corded or Braided Edge
The easiest way to create a contrasting-color edge is to tie two colors of yarn together in a slipknot and use them to do any kind of long-tail cast-on.
The yarn that goes over your thumb will be the color that creates the contrasting edge.
In the example on the left, the Long-Tail Cast-On was used. This creates a simple stripe.
In the example on the right, the Old Norwegian cast-on was used. This creates a thicker stripe.