The white lines you see are white, but the dark outlines of the animal such as the round the hand and eyes are punched through to show the background colour.
Oh I see. When you said the black lines couldn't be black, I thought you had used difference to make them white/transparent. I assumed the white lines had originally been black.
But this shirt is, amazingly, printed on unstiched material. And made into a t-shirt afterwards!!
Wow! That seems even weirder than printing the background color!! I don't know, I'm not all that familiar with how they make t-shirts these days. But that really seems like the long way around.
Ooooohhh! I guess they have websites these days, where you can submit your design and have bolts, or even huge rolls of fabric printed out with your design. It could be they used one of those sites. That would seem to explain it. Visitors can submit their own designs, or they can choose other people's designs, and buy the (I guess a bolt or even whole roll of) fabric. Or in some cases, as far as I understand, you can just buy products with the special printed fabrics. (I've seen scarves or sheets and pillowcases. But there could be sites that would sell t-shirts or other clothing.)
Well anyway, congrats on the design. Will you show us the next one too?
Now that I think about it, I wonder what kind of technology has made that cost-effective? It used to be next to impossible to get a job where you could create fabric designs (for printed designs). When I learned to sew clothing as a child/teenager (in the 70s), I always found it frustrating trying to find the kind of printed fabric I wanted. (Well, even now, sometimes I wonder what someone was thinking when they decided to buy or sell a fabric design.) You were pretty much limited to what the fabric stores sold, which was comparatively limited. And I used to dream about finding a job (when I grew up) where I could design fabrics - I was sure I could do a better job, haha! I guess I could design fabric prints to my heart's content now
(Hhmm...where's that to-do list....)