Using yarn A cast on 60 sts for leg and distribute sts over 4 needles, 15 sts on each. The beginning of the round will be between the first and fourth needle. Join to work in the round and work 4 cm in rib.
Work 1 round in st st.
Start following the colourwork chart from row 1 and repeat the 12 stitch pattern for 5 times. Work rows 2–38.
Row 39: Change to yarn A and k to end.
Row 40: K to end and at the same time work k2tog once on each needle = 56 sts.
Continue following the chart from row 41 and repeat the 8 stitch pattern for 7 times. Work rows 42–58.
Change to yarn A and work 4 rows in the following way:
Rows 59–60: K to end.
Row 61: K to end and at the same time work k2tog once on each needle = 52 sts.
Row 62: K to 2 last sts on the first needle, k2tog, k to beginning of the fourth needle, k2tog, k to end = 50 sts.
Reinforced heel flap
Start working the flap by knitting the sts of the first needle onto the fourth needle (= 24 sts). Turn work and leave the sts on the second and third needle on hold for a while.
Change to yarn C and start working the reinforced heel flap:
Row 1 (WS): Sl1 wyif, p to end. Turn work.
Row 2 (RS): *Sl1 wyib, k1*, repeat *-* to end. Turn work.
Repeat these 2 rows until you have worked them for 12 times (= 24 rows).
Next row: P to end.
Continue working in the reinforced stitch pattern shown for the heel and at the same time decrease for heel turn:
Next alternate decrease row (RS): Sl1, work to last 9 sts, skp. Turn work.
Next alternate decrease row (WS): Sl1, p6, p2tog. Turn work.
Next alternate decrease row (RS): Sl1, work to last 8 sts, skp. Turn work.
Keep working these decreases on each side of the 8 centre sts until you have only the 8 centre sts left. Now, divide these sts onto two needles, 4 sts on each.
Using yarn A and with the aid of the fifth needle, pick up 12 sts along the left edge of the heel flap + 1 st between the heel flap and the second needle and knit them through back loop onto the left heel flap needle. Knit the sts on the second and third needle. Pick up 1 st between the third needle and the heel flap + 12 sts along the right edge of the heel flap and knit them through back loop with the aid of the right heel flap needle. Knit the first 4 sts of the heel flap.
Change to yarn A and continue working with all 60 sts in st st. Start decreasing for the gusset:
Row 1: K to last 2 sts on the first needle, k2tog, work to the fourth needle, skp, k to end.
Row 2: K to end.
Repeat these 2 rows until you have 12 sts on each needle (= 48 sts).
Keep working straight in st st until the foot measures about 12 cm from the heel. After that, start following the chart from row 1 and repeat the 12 stich pattern for 4 times. Work rows 2–19.
Change to yarn G and use it for the rest of the work. Work straight until the foot measures ca. 20 cm or the little toe is covered. Then, start decreasing for the toe:
Row 1: First needle: K to last 3 sts, k2tog, k1; second needle: k1, skp, k to end; third needle: k to last 3 sts, k2tog, k1; fourth needle: k1, skp, k to end.
Row 2: K to end.
Repeat these 2 rows until you have 6 sts on each needle. After that, repeat only row 1 until you have 8 sts left. Cut yarn, thread through the stitches and pull tight. Weave in ends.
Make another sock to match.
Steam block gently.