There are 2 possibilities of how a design might be printed using the DTG printing method:
Dark/black garments - a layer of white underbase will be applied before applying the color layer, in order to achieve a more vibrant color outcome.
Light/white garments - only the color layer will be applied (no underbase).
Due to this, using gradients is not recommended when printing on dark garments. The white underbase layer will be somewhat visible in the final outcome.
What are the alternative design options?
The solution to using gradient designs on colored DTG products is to use halftone gradients, consisting of individual colored dots instead of one seamless color tone that gradually fades.
Here's an example of a halftone gradient (on the left):