Here is a step-by-step tutorial for making the Diagonal Half-and-Half Granny Square exactly like the picture.
I will break it into stitch counts, round-by-round instructions, corner placements, and color switching so you can follow easily.

🧶 FULL DETAILED PATTERN (US TERMS)

Colors:

Color A = Green
Color B = Pink

Square is made in two parts:
1️⃣ First make a triangle (Color A)
2️⃣ Then turn the triangle into a square (Color B)

✨ PART 1 — GREEN TRIANGLE (Color A)

Round 1 — Start the Triangle

Make a magic ring.
Ch 3 (counts as 1 dc).
Work 2 dc into the ring.
→ (This is your first cluster of 3 dc.)
Ch 2 (this is Corner 1).
Work 3 dc again into the ring.
Ch 2 (Corner 2).
Work 3 dc again.
Ch 2 (Corner 3).
Tighten the magic ring.
Sl st to top of starting ch 3.

📌 Stitch count: 3 corners, each with 3 dc.

You now have a small 3-sided granny triangle.

Round 2 — Expand the 3 Corners

Sl st across into the first corner ch-2 space.
In the corner space, work:
(3 dc, ch 2, 3 dc).
Along the next side, you will see 1 space (from round 1).
Make 3 dc into that space.
In the next corner:
(3 dc, ch 2, 3 dc).
Along next side: 3 dc in the space.
In the last corner:
(3 dc, ch 2, 3 dc).
Last side: 3 dc in side space.
Sl st to join.

📌 Triangle grows bigger.

Round 3 — Same Increase Method

Repeat the same pattern:

Every corner space:
→ (3 dc, ch 2, 3 dc)

Every side space:
→ 3 dc

● In this round, each side will now have 2 side spaces.

Round 4 — Same Pattern

Repeat again.

● Every round adds +1 more side space per side.
● Still working in a triangle shape.

Round 5 — Last Green Round

Repeat corner + side repeats:

Corners: (3 dc, ch 2, 3 dc)
Sides: 3 dc in each space

Now you have a large green triangle like the picture.

✨ PART 2 — ADD PINK TO TURN TRIANGLE INTO A SQUARE

We now attach Color B (pink).

Choose any corner of the triangle.
We will now create 4 corners instead of 3 → this transforms triangle → square.

⭐ PINK ROUND 1 — Create a Square Shape

Attach yarn in a corner ch-2 space.

New Square corners:

● One corner goes on each triangle corner
● The fourth corner will be created at the middle of the long straight edge

Work this round like this:

Corner 1 (triangle corner)

Work: (3 dc, ch 2, 3 dc)

Side 1 (has several spaces)

Make 3 dc in each side space from the green triangle

Corner 2 (triangle corner)

Work: (3 dc, ch 2, 3 dc)

Side 2

Again make 3 dc in each space

❗ Corner 3 — the NEW corner

This corner is created at the middle point of the long side:

When you reach the center, work ch-1, skip 1 space, then:
(3 dc, ch 2, 3 dc)
This creates the 4th square corner.

Side 3

3 dc in each space until next triangle corner

Corner 4 (triangle corner)

Work: (3 dc, ch 2, 3 dc)

Sl st to join.

✔ Now your shape is a perfect square.

⭐ PINK ROUND 2 — Build the Square Bigger

Now it becomes a normal granny square.

For every corner ch-2 space:
→ (3 dc, ch 2, 3 dc)

For every side space:
→ 3 dc

Work all the way around.

⭐ PINK ROUND 3 — Optional (For Size)

Repeat: