I prefer doing the entire blanket whole and avoiding the seaming.
Via intarsia. CO x stitches of each color, one after the other. Work Y rows to form a square. Cut yarns and rearrange color order. Reattach yarns on next row. Work Y rows. Repeat. To get something like this.
Or this, which requires "picking up stitches" after turning each corner, but no seperate seaming.
Or, try enterlac.
Or, a large basketweave pattern.