You will need 2 colours for this square.
Cast on -
Aran weight 5mm needles cast on 20 stitches using 1 colour only
Double knitting 4mm cast on 24 stitches using 1 colour only
Abbreviations
c1 - first colour
c2 - second colour
Pattern
Row 1 - *k2(c1) k2(c2)* repeat *-* until end of row
Row 2 - *p2(c2) p2(c1)* repeat *-* until end of row
Row 3 - *k2(c2) K2(c1)* repeat *-* until end of row
Row 4 - *p2(c1),p2(c2)* repeat *-* until end of row
Repeat rows 1 - 4 until your work measures 4" Cast off.