Check stitch - Simple slip stitch pattern and easy to knit in two color.

Color A, cast on a multiple of 4 sts.
Row 1 - RS: Color A, knit
Row 2: Color A, purl.
Row 3: Color B, k3, * sl 2 wyib, k2; rep from * to last st, k1.
Row 4: Color B, p3, * sl 2 wyif, p2; rep from * to last st, p1.
Row 5: Color A, knit.
Row 6: Color A, purl.
Row 7: Color B, k1, * sl 2 wyib, k2; rep from * to last 3 sts, sl 2 wyib, k1.
Row 8: Color B, p1, * sl 2 wyib, p2; rep from * to last 3 sts, sl 2 wyif, p1.
Repeat Rows 1 - 8.

Knitting abbreviations:
K: Knit | P: Purl | Sl: Slip stitch
Wyif: With yarn in front | Wyib: With yarn in back.