I managed to finally finish this square, and to do so before nightfall.

To start, ch 4 and join with sl st to first ch.

Round 1: Work 8 sc into the ring just made. Join with slip st to first sc.

Round 2: Ch 3 (Counts as first dc), dc into joining st, ch 1, *2 dc into next st, ch 1, repeat from * 6 times more. Join with sl st to first st. Finish off.

Round 3: With new color make sc into the right hand dc of any 2-dc group, sc into next dc, sc into ch-1 sp, 1 long sc in same st as 2-dc group, *sc in next two dc, sc into ch-1 sp, 1 long sc in same st as 2-dc group, repeat from * six times more. Join with sl st to first sc made. Finish off. (24 sc & 8 long sc)

Round 4: With a new color, work a sc into the back ridge of each of the sc and long sc of previous round. Join with sl st to first sc made. Fasten off. (32 sc)

Round 5: With new color and in any stitch, work *(sc, ch2 sc), sc in next st, [2sc in next st, sc in next st], repeat from [ to] twice more; repeat from * 3 times more, join with sl st to first sc made. Fasten off. (48 sc, 4 ch-2 sp).

Round 6: With new color in any ch-2 sp work *(2dc, ch 2, 2dc), dc in next 2 sts, hdc in next 2 sts, sc in next 3 sts, hdc in next 2 sts, dc in next 2 sts, repeat from *3 times more. Join with sl st to first dc made. Fasten off. (60 sts, 4 ch-2 sp)

Round 7: With a new color and in any ch-2 sp * work 2sc into ch-2 space, make 2 sc in next st, make sc in each of next 13 sts , make 2 sc in next st, repeat from * 3 times more. Join with sl st to first sc made. Finish off. (78 sc)

Corners:

Row 1: With the right side facing, attach yarn with a sc to the third sc from the right of any corner. Sc in the next 12 sts. (13 sc) Ch1, turn.
Row 2: Sc first two stitches tog. Sc in next 9 st, sc tog last two stitches (11sc). Ch 1, turn.
Row 3: Sc first two stitches tog. Sc in next 7 st, sc tog last two stitches (9sc). Ch 1, turn.
Row 4: Sc first two stitches tog. Sc in next 5 st, sc tog last two stitches (7sc). Ch 1, turn.
Row 5: Sc first two stitches tog. Sc in next 3 st, sc tog last two stitches (5sc). Ch 1, turn.
Row 6: Sc first two stitches tog. Sc in next 1 st, sc tog last two stitches (3sc). Ch 1, turn.
Row 7: Sc next 3 sts tog. (1 sc). Finish off.

Repeat with the 3 remaining corners.

Border:

Round 1: Attach new yarn the top of any of the triangles just completed (Ch 3 counts as first dc) *at the top of the triangle work (3 dc, ch 3, 3 dc), working along the side, evenly space 8 3 dc groups, repeat from * 3 times more. Join with sl st to first dc made. Finish off.

Round 2: Using a new color, attach yarn in any ch-3 space. (Ch 3 counts as first dc), *work (3dc, ch 3, 3dc) in the ch-3 space, work 3dc between each 3dc group, repeat from * 3 times more and join with st st to first dc made. Fasten off.

When you are done, you will have something that looks like this:

As it happens, the C squares are one of my favorites. I particularly like working the four triangular corners and enjoy the way the colors in the corners work with the colors of the border.