The pattern

Knit

Multiple of 3

Cast on in color A.

Row 1 (RS): Using color A, K1, *sl 1, K2; rep from * to last 2 sts, sl1, K1.

Row 2: Using color A, Purl.

Row 3: Using color B, *sl 1, K2; rep from * to end.

Row 4: Using color B, Purl.

Rep these 4 rows.