lol
Sorry, someone else may be able to put it clearer.
I would cut sashings at 1.5 inches, and attach to all four sides of the block. After sewing, your visible sash on one block will be 1.25 inches.
Do this with all the blocks.
Then, trim each one to the same size. So measure them all, pick the smallest and use that as a template to trim the others. You now have them all the same size. The difference in the sashing widths after trimming won't be visible to the naked eye, unless it's horrific (like a full inch or something).
Once you sew each block to the other, you'll lose another seam allowance, so the sashing on one side of one block will be a visible 1 inch (roughly). Join to the next block with it's one inch sashing, and you will have a two inch strip of colour between each block.
Is that better?
:-)