This afghan is called mile a minute because of how fast you can crochet each strip.
Size J hook (6mm)
Row 1: in 7th ch from hook, 2dc ch1 2dc sl st in last ch, ch3 turn.
Row 2: ch3, skip 2dc, 2dc ch1 2dc in the ch1 sp, 1dc in last sp, ch3 and turn.
continue row 2 till you have a strip about 4 inches less than your overall desired length, and tie off.
Tie on new color in any ch3 or dc sp, pull up a loop and 1dc in same sp, 2dc in each ch3 or 1dc sp to end of strip, evenly placeing 13dc in each end of strip, end with sl st to join, and tie off.
crochet each strip together with wrong sides facing each other, working only the flat sides of each strip.
I single crochet in each stitch around placing extra stitches in the corners so they will not curl, and end with sl st to join. You may use any border you like to make this mile a minute afghan yours.
Work in ends.