Those are Great color combos !!
If you want to add sashing, make strips as long as the blocks are wide , add to 1 side of each block, then a couple of options for other side, depending if you want a different color in the corners, or solid for solid add a piece wide as both together. can also use one solid strip, but use lost of care when putting together or can get wonky.
Good Luck no matter what you do will turn out Great!!