Halftones and gradients in t-shirt printing are made by the printers spraying down layers of ink onto the shirt. On dark shirts, the printers put down a base white layer first, which sits underneath the colored layers, so the printers are effectively trying to lay down two layers over the exact same spot.
When using gradients and halftones in your design, it's worth keeping the following in mind:
Black fading to nothing |
Ok |
White fading to nothing |
Tricky |
Color fading to nothing |
Tricky |
Color fading to another color |
Ok |
It’s a little complicated to remember those details so we usually recommend halftones over gradients. Feel free to read more on halftones here.