The sad thing is your leftovers will be adifferent dye lot . Why not look for some galss tile in the same size and install with matching grout

Take a look at Fireclay and Pratt & Larson:

Tile Colors | Fireclay Tile

Handmade Ceramic Tile Products - Pratt + Larson (prattandlarson.com)

Also look at:

Encore Tile

Sonoma Tilemakers

They might like Bedrosians Marin Misty Blue (comes in square, rectangular, and edge pieces) or Renzo Sky (square, rectangle, picket, edge) but only if they want some variation - both of those are variation level V4.

In any case, I'd encourage them to order lots of samples and view in their own lighting.