More secondary shapes, too, with crosses creating crosses.
I really like the way that the diagonal lines carry through from block to block, which I think is easier to see in this pared-back palette (with only 3 colours).
Those lines also present an opportunity for playing with transparency. I had to use a different colour palette to show you what I mean: red paired with white produces pink crosses where the shapes overlap.
Expanding the colour palette pushes those diagonal lines to the background and brings the individual blocks to the fore.
Those corner bits on each block can be coloured differently too, just to mix things up a bit. I’d be tempted to stick with a limited palette, like the one shown below. Or you could expand the palette but make all those corners the same colour. Otherwise, I think it could all get very busy, very fast.
This design would be relatively easy to translate into an actual quilt. It’s mostly standard blocks and shapes, with a few fiddly bits along the way.