Special Stitch:

FRONT-POST TREBLE - YO twice, insert hook around the post of the dc in the row  below, (from front to back then to the front of the work). The post of the stitch is laying across the top your hook. YO, pull up a loop.  You now have 4 loops on your hook.  Work the same as a normal treble crochet stitch.  YO, pull through 2 loops on hook, 3 times. 

Instructions:

With white  ch  4, sl st in first ch to form ring.

Rnd 1: Ch 3, 2 dc in ring, *ch 3, 3 dc in ring; rep from * twice more;  ch 1, hdc in 3rd ch of beg ch 3 to form last ch-3 sp. (12 dc, 4 ch-3 sps).

Rnd 2: Ch 3, 2 dc in same sp, ch 1, *(3 dc, ch 3, 3 dc) in next corner sp, ch 1; rep from * twice more; 3 dc in next ch 2 sp, ch 1, hdc in 3rd ch of beg ch 3 to form last ch-3 sp. (24 dc, 4 ch-3 sps.)

Rnd 3: Ch 3, 2 dc in same sp, ch 1, *3 dc in next ch 1 sp, ch 1, (3 dc, ch 3, 3 dc) in next ch 2 sp, ch 1; rep from * twice more; 3 dc in next ch 1 sp, ch 1, 3 dc in next  ch 2 sp, ch 1, hdc in 3rd ch of beg ch 3 to form last ch-3 sp. Finish off   white.

Rnd 4: Join red with a sc in any corner sp, 2 sc in same sp (3 sc corner), *sc in each of 3 dc,  FPTR (see Special Stitch) around the center dc of the 3 dc group on  rnd 2, sc in next 3 dc, FPTR around the center dc of the 3 dc group on Rnd 2, sc in next 3 dc, 3 sc in next corner sp; rep from * around, join with a sl st to first sc. Finish off  red.

Rnd 5: Join white with a slip stitch in second sc of any corner. Ch 3 -counts as first dc-, ( 1 dc, ch 2, 2 dc) in same st, *dc in each st across (13 dc) to the 2nd sc of the next corner, (2 dc, ch 2, 2 dc) in next st; rep from * around, join with  sl st to top of beg ch 3.

Rnd 6: Sl st to the ch 2 corner sp. Ch 3 -counts as first dc-, (1 dc, ch 2, 2 dc) in corner sp, ch 1, *work skip next stitch, dc in next dc, ch 1 across to next corner, (2 dc, ch 2, 2 dc) in corner sp; rep from * around. Join with a sl st in 3rd ch of beg ch 3. Finish off  white.

Rnd 7: Join royal blue with a sc in corner sp, 2 sc in same sp, *sc in next 2 dc.  Working in front of sp on Rnd 6, (dc into top of skipped dc on Rnd 5, sc in next dc) 9 times; sc in next dc, 3  sc in next corner sp, rep from * around. Join with a  sl to to first sc. Finish off   blue.

When you complete this round your square will measure  7". You can stop here if you want a smaller square but for a WTC 12" square continue on with  Rnd 8.

Rnd 8: Join white in any corner center sc,  ch 3 -counts as first dc-, (1 dc, ch 2, 2 dc) in same st, *dc in each  st to next corner sp, (2 dc, ch 2, 2 dc) in corner sp; rep from * around.  22 dc across

6 inch variation

Rnd 5: sc around, 3 sc in corners.