The instructions for making the rectangles are as follows:
Foundation Rows and Round 1


















Round 2










Work 2 hdc, ch2 in the corner where you started and ss into the beg-ch.
Continue to make 25 rectangles in each of the four colours.


Arrangement of Rectangles
You can arrange your rectangles as you please. I arranged mine as follows:

Joining the Granny Rectangles
The Rectangles are joined using the joining colour (E), which is Graphite in my sample. I used the join-as-you-go joining method, which meant that each rectangle was joined to the adjacent rectangle whilst the third round was added to each rectangle. The third round is worked in the same way as for the second round, but with an additional hdc cluster along each side.
The join-as-you-go joining method is outlined here. The principles of this tutorial are adapted to apply to the rectangles rather than squares.

Border
The border is simply 6 rows of hdc clusters (a group of 2 hdc), all worked in the joining colour E (Graphite).

Border round 1: Using yarn E (Graphite), pull up a loop in any ch2 corner space. Ch2 (counts as first htr), 1 hdc into same space, work along the side of the blanket inserting *2 hdc in each space formed between the hdc clusters from the row below. When you come to the join between the two rectangles insert a hdc cluster in the corner space of both the first rectangle and the second (see photo below). When you arrive at the corner of the blanket work (2 hdc, ch2, 2 hdc) in the corner* and then repeat from *to* until you reach the start of the round, 2 hdc in corner space where you started, ch2, ss into top of beg-ch.

Border Round 2: Turn the blanket over, ss into the chain 2 corner space that you just formed. Ch2 (counts as 1htr), 1 hdc into same space, work along each side of the blanket working 2 hdc in each space formed between the treble clusters from the row below and working [2 hdc, ch2, 2 hdc] in each corner. When you reach the start of the round, 2 hdc in corner space where you started, ch, ss into the top of the beg-ch.
Border Round 3-6: Repeat Border Round 2.
Fasten off and weave in all ends. I don’t usually block my blankets, but you can do this if you wish.