I am experimenting with colour graduation and I made this using only 2 colours.
To make the yarn thick enough to be a useful rug I worked 4 strands together, changing the combination to get the colour graduation. It worked up quite quickly, but I ran out of yarn which delayed completion.
I wanted something cool, light and quite sophisticated while remaining true to the craft.

Note

I frogged the outer rows quite a few times to get it to lie flat - which was a mammoth task with 4 strands of yarn!
In the end the sequence of rows that I did to get the right size, and it laid flat afterwards, was as follows (if you have followed the pattern hopefully my numbering should make sense):
Followed pattern to last row before the border, then:
3 more rounds of 3 in each ch sp
1 round of (2,ch,2) in each ch sp
3 rounds of 2 in each ch sp
1 round of 3 in each ch sp
then onto the border as charted.

This does change the look of the pattern as the spiral effect is lost in the outer rings which you can see on my pics. However, I don’t think that matters. Key thing is to limit your increases in the outer rounds as it is too many stitches that causes the frilling.