I really, really like gingerd's idea of the different sizes on the batik with the tiny black sashing. Nice way to show off the shirts but give it an overall look. This site is just so full of creative people and wonderful new ways to look at things!

That's going to make a nice quilt. I'd go bold and use black and pink. I'd surround the dark squares with pink and the light ones with black, making the sashings different sizes so the sashed blocks can then be sewn directly together.

That looks so nice!

How about a shadow quilt? Black or dark gray works best for the shadow, but really any dark fabric that contrasts would work. Light background is needed for contrast.

edited to add: I just noticed the black shirt. Just put a border on it to add contrast. See the light shirt that has a grey border on the bottom picture.

you've got a lot of good suggestions...but what about no filler? I did one like that and my niece really liked it. I used the sleeves from the shirts for the piano keys border

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I was going to suggest doing what Mayert said. I was looking for my picture like that. If you really want to use sashing I would use a mottled purple, or batik. Something dark. I feel black would be too harsh.

Have you tried putting the black T-shirt in the center, then framing it out in pink; then make all the other sashing in black?

A medium gray would look great. In the lower left square is a circle of gray
that has the words 'I believe' in it and also in the center the fire hose ribbon
has a matching gray. And, of course, gray and pink is a classic combo.
I vote for gray!

My vote is for grey. When I made a chemo quilt for a friend with breast cancer, she wanted it a variety of pink fabrics. So I did, and used Zen Grey by Moda for sashing. Love it. There's a soft sophistication to it.

How about a batik that has more than one of the colors? Pink and blue? Pink with lavendar? Pink with black?