When it comes to printing light or white garments, the settings should be basically the same as printing on light cotton. You may need to slightly lower the ink volume if there is any bleeding in the print, but little else will change. Depending on your RIP software, you may reduce the ink percentage, or try printing in a lower resolution as well.
Printing on dark garments does require different print settings from what you use for cotton prints. The most important difference here is the white ink. You need to increase the amount of white ink printed compared to a cotton print. The color pass should still stay the same. For example, the settings on cotton are commonly 1,440 X 1,440 or 1,440 X 720 resolution. You will get an increased amount of white ink by changing the resolution to 2,880 X 1,440 or 2,880 X 720.
—Paul Green, OmniPrint International